F irearms have a unique significance in American society. Millions own or use firearms for numerous lawful purposes, such as hunting and protecting themselves in the home. Still, firearms annually cause tens of thousands of injuries and deaths, including in high-profile mass shootings. The widespread lawful and unlawful uses of firearms have prompted vigorous debate over wheth er further firearm regulation would be effective or appropriate. And framing the policy debate are legal issues stemming from the existing federal framework of firearms laws and the constitutional constraints that may cabin Congress's ability to legislate in this area. Firearms regulation at the federal level has grown more expansive over time, setting rules for the lawful manufacture, sale, and possession of firearms at the national level. These federal firearms laws mostly serve as a baseline that states can (and sometimes do) supplement, and Congress regularly considers legislation to address perceived gaps in these laws. Proposals to modify the current federal framework for regulating firearms may be informed by numerous constitutional considerations, including the scope of the Second Amendment right to keep and bear arms and the need to ground legislation in one of Congress's enumerated powers. This report provides an overview of the development of federal firearms laws and the major components of the current statutory regimes governing firearms. It then describes the constitutional considerations that may impact Congress's ability to enact firearms laws. Finally, this report describes selected topical areas where the 115 th and 116 th Congresses have considered legislation to amend the existing federal framework regulating firearms, highlighting some of the constitutional issues that may arise in those areas. Federal laws regulating firearms date back roughly a century, and over time lawmakers have established more stringent requirements for the transfer, possession, and transportation of firearms. Though not a regulation of firearms per se, an excise tax was levied on imported firearms and ammunition beginning in 1919. In 1927, a federal law was enacted prohibiting the use of the U.S. Postal Service to ship concealable firearms. Then, "[s]purred by the bloody 'Tommy gun' era" of the 1920s and early 1930s, Congress passed the National Firearms Act of 1934 (NFA), which established a stringent taxation and registration scheme for specified weapons associated with the Prohibition-fueled gang violence of the time. A few years later, Congress enacted the Federal Firearms Act of 1938 (FFA), which created a licensing scheme for the manufacture, importation, and sale of firearms and established limited categories of persons who could not possess firearms. The FFA eventually was superseded, however, by the more comprehensive Gun Control Act of 1968 (GCA). In addition to expanding the FFA's licensing scheme and categories of prohibited persons—which largely had been restricted to certain criminals—the GCA augmented the criminal penalties available for violations and established procedures for obtaining relief from firearm disabilities. Since the GCA's passage, intervening legislation has amended the regulatory regime significantly. For instance, the Firearm Owners' Protection Act of 1986 (FOPA) carved out exceptions to the felony firearm prohibition for certain crimes, repealed certain regulations pertaining to ammunition, expressly prohibited the creation of a national gun registry, added additional categories of persons who are barred from possessing firearms, prohibited the private possession of machineguns manufactured on or after the date of FOPA's enactment, and further expanded the available criminal penalties for violations, among other things. Additionally, the Brady Handgun Violence Protection Act of 1993 (Brady Act) mandated that the Attorney General create a background check system—the National Instant Criminal Background Check System (NICS)—which queries various government records that could indicate that a prospective transferee is ineligible to receive a firearm. The Brady Act further required that a background check be run for many, but not all, proposed firearms transfers before they can be completed. And the Gun-Free School Zones Act added a provision to the GCA that, subject to certain exceptions, bans firearms in statutorily defined school zones. In 1994, Congress also imposed a 10-year moratorium on the manufacture, transfer, or possession of "semiautomatic assault weapons," as defined in the act, and large capacity ammunition feeding devices, but the ban was permitted to expire in 2004. Finally, some piecemeal legislation in recent years has sought to protect lawful firearm owners, manufacturers, or dealers in certain ways. For example, the Protection of Lawful Commerce in Arms Act, enacted in 2005, grants civil immunity to firearm manufacturers, dealers, and importers when weapons made or sold by them are misused by others. Firearms regulation in the United States is an area of shared authority among federal, state, and local governments. Individual states have enacted a variety of laws relating to the possession, registration, and carrying of firearms, among other things. However, federal law establishes a baseline regulatory framework that state and local laws may not contradict. Thus, the current collection of federal firearms laws may be thought of as a regulatory floor that sets out, at the federal level, the minimum requirements for lawful manufacture, sale, and possession of firearms. The two principal federal firearms laws currently in force are the NFA and the GCA, as amended. The Department of Justice's Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is the principal agency charged with administering these laws. The NFA was the first major piece of federal legislation regulating the sale and possession of firearms. Through a taxation and registration scheme, the law sought to curb the rise of violence connected to organized crime by targeting the types of weapons that (at the time of passage) were commonly used by gang members. In its current form, the NFA regulates the manufacture, transfer, and possession of certain enumerated weapons deemed to be "particularly dangerous" : (1) short-barreled shotguns, defined as having a barrel length under 18 inches; (2) short-barreled rifles, defined as having a barrel length under 16 inches; (3) modified shotguns or rifles with an overall length under 26 inches; (4) machineguns, defined as weapons—including frames or receivers—that shoot "automatically more than one shot, without manual reloading, by a single function of the trigger," as well as parts intended to convert other weapons into machineguns; (5) silencers; (6) "destructive devices," including bombs, grenades, rockets, and mines; and finally (7) a catchall category of "any other weapon" that is "capable of being concealed on the person from which a shot can be discharged through the energy of an explosive," among other things. The NFA explicitly exempts from regulation antique firearms and other devices that are primarily "collector's item[s]" not likely to be used as weapons. All NFA firearms that are produced or imported—as well as their manufacturers, dealers, or importers—must be authorized by and registered with the Attorney General (previously, the Secretary of the Treasury). Any transfer of an NFA firearm must likewise be accompanied by a registration in the name of the transferee. The registrations of all NFA firearms not in the possession or under the control of the United States are maintained in a central registry, and all persons possessing NFA firearms must retain proof that such firearms have been registered. Any NFA firearm that is produced or imported must be identifiable, with firearms that are not destructive devices bearing, among other things, a serial number that "may not be readily removed, obliterated, or altered." Every importer, manufacturer, and dealer in NFA firearms must pay an annual "special (occupational) tax for each place of business," and a separate tax must also be paid for each firearm made. Upon transfer of an NFA firearm, the transferor is subject to a tax of a varying amount depending on whether the firearm to be transferred falls under the catchall category of "any other weapon." A number of tax exemptions exist. Most notably, firearms made by or transferred to the United States, any state, any political subdivision of a state, or any official police organization engaged in criminal investigations are exempted, as are firearms made by or transferred between qualified manufacturers or dealers. A person who violates or fails to comply with the requirements of the NFA is subject to a fine of up to $10,000, imprisonment for up to 10 years, or both. Firearms involved in violations are also subject to forfeiture. To be criminally culpable for a violation of the NFA, one generally must have knowledge of the features of the firearm that make it a "firearm" under the statute, but one need not know that such a firearm is unregistered. As originally enacted, a person compelled by the NFA to disclose possession through registration could then be prosecuted if the registration reflected that the person was barred by other legal provisions from possessing firearms. However, the Supreme Court ruled in Haynes v. United States that this forced disclosure of potentially incriminating information violated the Fifth Amendment to the U.S. Constitution, which provides in part that no person "shall be compelled in any criminal case to be a witness against himself[.]" Haynes prompted Congress to amend the statute to make clear, among other things, that no information from registration records that are required to be submitted or retained by a natural person may be used as evidence against that person in a criminal proceeding for a violation of law occurring prior to or concurrently with the filing of the records, unless the prosecution relates to the furnishing of false information. As amended, the Court has rejected a subsequent challenge to the NFA on Fifth Amendment grounds. Congress passed the GCA in the wake of the assassinations of Dr. Martin Luther King Jr. and Senator Robert Kennedy to "keep firearms out of the hands of those not legally entitled to possess them because of age, criminal background, or incompetency and to assist law enforcement authorities in the states and their subdivisions in combating the increasing prevalence of crime in the United States." Among other things, the statute represented "a Congressional attempt to stem the traffic in dangerous weapons being used in an increasing number of crimes involving personal injury." As enacted, the GCA expanded the existing licensing scheme for the manufacture, importation, and sale of firearms and augmented a previously enacted prohibition on the possession of firearms by certain categories of persons (including felons and "mental defective[s]"). It also supplemented available criminal penalties and established procedures for obtaining relief from firearms disabilities. The GCA today is not a single statute but rather a complex statutory regime that has been supplemented regularly in the decades since its inception. Broadly speaking, the GCA, as amended, regulates the manufacture, transfer, and possession of firearms, extending to categories of weapons that fall outside the scope of the NFA. In general terms, the GCA sets forth who can—and cannot—sell, purchase, and possess firearms; how those sales and purchases may lawfully take place; what firearms may lawfully be possessed; and where firearm possession may be restricted. Major components of the GCA and related supplementing statutes are discussed below, focusing on (1) licensing requirements for firearm manufacturers and dealers, (2) prohibitions on firearm possession, (3) background checks for firearm purchases, (4) interstate firearm sales and transfers, and (5) penalties. The GCA regulates the manufacture and sale of firearms by requiring persons and organizations "engaged in the [firearms] business"—that is, importers, manufacturers, and dealers—to obtain a license from the federal government and pay an annual fee. These persons and entities are commonly known as Federal Firearm Licensees, or FFLs. Applicants must meet various requirements to become FFLs, including being at least 21 years of age, maintaining a premises from which to conduct business that meets safety standards, and certifying compliance with applicable state and local laws. Upon licensing, FFLs are subject to recordkeeping and reporting obligations with respect to the disposition of firearms to non-FFLs and must identify imported or manufactured firearms by means of a serial number, among other things. FFLs also must comply with background-check requirements and certain other transfer restrictions discussed in more detail below. An FFL who willfully violates any provision of the GCA or implementing regulations may, after notice and opportunity for hearing, have his or her license revoked. In this context, a "willful" violation means that the FFL purposefully disregarded or was plainly indifferent to his or her known legal obligation. A key question with respect to the GCA's licensing regime is what it means to be "engaged in the [firearms] business." Manufacturers are considered to be "engaged in the business" if they "devote time, attention, and labor to manufacturing firearms as a regular course of trade or business with the principal objective of livelihood and profit through the sale or distribution of firearms manufactured." And dealers are considered to be "engaged in the business" if they "devote[] time, attention, and labor to dealing in firearms as a regular course of trade or business with the principal objective of livelihood and profit through the repetitive purchase and resale of firearms." A person is not "engaged in the business" of dealing in firearms, however, if that person "makes occasional sales, exchanges, or purchases of firearms for the enhancement of a personal collection or for a hobby, or who sells all or part of his personal collection of firearms." Accordingly, if a person falls within this definitional exclusion, he or she is not subject to the licensing regime and other FFL requirements, such as conducting background checks. There have been a number of court decisions shedding further light on what it means to be "engaged in the business" of dealing in firearms under the GCA, which is a fact-specific question that is dependent on the particular circumstances of the case. Even though the statute mandates that, to require a license, the dealer's principal objective in selling firearms must be livelihood and profit, courts have recognized that firearms sales need not be the person's sole source of income or main occupation. Instead, relevant factors include (1) the quantity and frequency of firearms sales; (2) sale location; (3) how the sales occurred; (4) the defendant's behavior before, during, and after the sales; (5) the type of firearms sold and prices charged; and (6) the defendant's intent at the time of the sales. At least one federal appellate court appears to apply a broad standard, requiring the government to prove only that the defendant holds himself out as a source of firearms. Furthermore, because the number of firearms sold is typically only one of many factors courts consider, convictions under the GCA for unlawfully dealing in firearms without a license have been sustained for as few as two or four firearms sales. The GCA regulates firearm possession in several ways. Principally, the statute establishes categories of persons who, because of risk-related characteristics, may not possess firearms. Possession of certain types of firearms, as well as possession of firearms in certain locations , also are restricted. Under the GCA, it is unlawful for a person who falls into at least one of nine categories to ship, transport, possess, or receive any firearms or ammunition. Specifically, a person is prohibited if he or she is a felon (i.e., someone who has been convicted in any court of a crime punishable by a term of imprisonment exceeding one year); is a fugitive from justice; is an unlawful user of, or is addicted to, any controlled substance; has been adjudicated as a "mental defective" or committed to a mental institution; has been admitted to the United States pursuant to a nonimmigrant visa or is an unlawfully present alien; has been dishonorably discharged from the Armed Forces; has renounced his or her U.S. citizenship; is subject to a court order preventing that person from harassing, stalking, or threatening an intimate partner (or that partner's child) or engaging in other conduct that would cause the partner to reasonably fear bodily injury to himself or herself or the child; or has been convicted in any court of a misdemeanor crime of domestic violence. A separate GCA provision prohibits anyone—not just FFLs—from selling or otherwise disposing of a firearm if that person knows or has "reasonable cause" to believe that the prospective recipient fits into any of the above categories. Additionally, a person under indictment for a crime punishable by a term of imprisonment exceeding one year is not barred by the GCA from possessing a firearm but may not receive, ship, or transport a firearm. In other words, a person who has been charged with a felony need not forfeit already-owned firearms, but he or she may not acquire new ones while the charges are pending. The GCA also places significant restrictions on the transfer to, and possession of, firearms by persons under the age of 18. Because a number of the terms in the individual prohibitions of Section 922(g) are not defined by statute, the contours of some of the prohibitions have had to be fleshed out by regulations and judicial construction. Some of the interpretative issues raised with respect to these prohibitions are discussed briefly below. " Possession " by a prohibited person . For possession of a firearm by a prohibited person to be unlawful, that possession may be "actual" or "constructive." Actual possession occurs when a person exercises physical control over a firearm. Constructive possession exists when a person has the power to exercise dominion and control over a firearm directly or through others. For example, actual possession may be found when, during a traffic stop, a police officer pats down the driver and discovers a firearm in the driver's waistband. Constructive possession, on the other hand, may be found when, during a traffic stop, an officer observes a firearm not on the driver's person but elsewhere inside the vehicle. Although proximity to a firearm, alone, is insufficient to establish constructive possession, the totality of the circumstances—including other evidence of a connection to the firearm, movements implying control, or the defendant's activities before and after the discovery—is used to establish constructive possession. Persons prohibited due to a conviction for a felony or misdemeanor crime of domestic violence "in any court . " The prohibitions on possession of a firearm by a person convicted of a felony or a misdemeanor crime of domestic violence "in any court," which are among the most frequently enforced prohibitions in the statute, raise the question of what constitutes "any court." Initially, federal courts took an expansive view of the term. For instance, in holding that a military court-martial is a court within the meaning of the GCA, a 1997 opinion from the Seventh Circuit Court of Appeals used the dictionary definition of the word any : Looking to section 922(g)(1), we find nothing that defines or limits the term "court," only a requirement that a conviction have been "in any court" in the course of prohibiting possession of firearms by a felon. Certainly "any court" includes a military court, the adjective "any" expanding the term "court" to include "one or some indiscriminately of whatever kind"; "one that is selected without restriction or limitation of choice"; or "all." Additionally, some federal courts had concluded that a conviction in "any court," for the purposes of determining a firearm disability, included convictions in foreign courts. But in resolving a circuit split over this issue, the Supreme Court interpreted the phrase to cover only domestic convictions in its 2005 ruling Small v. United States . In a 5-4 decision, the Court adopted a more limited interpretation of the GCA's reference to "any" court than employed by the Seventh Circuit and other lower courts. In reaching its conclusion, the Court applied the legal presumption that "Congress ordinarily intends its statutes to have domestic, not extraterritorial application." The Court ruled that this presumption against extraterritorial application was particularly relevant to the GCA, given the many potential differences between foreign and domestic convictions and "the potential unfairness of preventing those with inapt foreign convictions from possessing guns." The Court additionally reasoned that nothing in the GCA's text or legislative history suggests that the act was intended to allow foreign convictions to give rise to a firearms disability. Although the Supreme Court's opinion in Small abrogated lower court rulings holding that foreign convictions serve as a predicate offense for the GCA's firearm ban for felons, the opinion did not directly disturb earlier rulings holding that U.S. military convictions count for the ban. And a conviction by a court-martial does not appear to raise any of the concerns mentioned by the Supreme Court in Small about foreign convictions. Federal courts have not found tension with Small when analyzing the related issue of whether a court-martial conviction is encompassed by the term any court in statutes that provide heightened penalties for certain repeat offenders. For instance, the Eighth Circuit opined that courts-martial proceedings maintain a connection to the U.S. government, given that they were created by Congress and are governed by federal statute. And the Fourth Circuit reasoned that, although there are some differences between courts-martial and civilian courts, they do not "rise to the level of contrasts between domestic and foreign courts that Small highlighted." Accordingly, a conviction by a court-martial for a crime punishable by a term exceeding one year or a misdemeanor crime of domestic violence likely would qualify as a conviction in "any court" for the purposes of the GCA's firearm disqualifiers. Prohibition applicable to nonimmigrant visa holders . With respect to the prohibition for aliens admitted to the United States pursuant to nonimmigrant visas, the terms of the provision do not explicitly prohibit firearm possession for aliens otherwise admitted (e.g., those admitted on an immigrant visa, through the Visa Waiver Program, as refugees, or without a visa for brief visits for business or tourism by Canadian citizens and certain residents of the Caribbean islands). Initially, ATF interpreted the GCA provision barring firearm possession for aliens admitted on nonimmigrant visas as encompassing all foreign nationals in nonimmigrant status in the United States, including those categories of nonimmigrant aliens who do not need a visa to enter the United States. ATF reasoned that Congress intended for the prohibition to cover all nonimmigrant aliens, given that a nonimmigrant visa is needed for fewer than 50% of nonimmigrants entering the United States and merely "facilitates travel" rather than conferring nonimmigrant status. However, the DOJ's Office of Legal Counsel (OLC) overruled ATF's interpretation in 2011. "The text is clear," OLC said, "the provision applies only to nonimmigrant aliens who must have visas to be admitted , not to all aliens with nonimmigrant status." Additionally, OLC rejected ATF's contention that "applying the [firearm] prohibit[ion] to only a particular subset of nonimmigrants would produce 'irrational' results." Rather, OLC opined that Congress could have rationally concluded that nonimmigrants eligible for admission without a visa are less of a public safety risk or that nonimmigrants on brief visits to the United States may be less likely to purchase a firearm. In response, ATF issued a final rule imposing the firearm prohibition on only those nonimmigrants admitted to the United States with a nonimmigrant visa. ATF further announced that "[n]onimmigrant aliens lawfully admitted to the United States without a visa, pursuant either to the Visa Waiver Program or other exemptions from visa requirements, will not be prohibited from … possessing firearms." Prohibition applicable to those who unlawfully use or are addicted to a controlled substance . The prohibition on firearm possession by those who unlawfully use or are addicted to controlled substances also raises the question of what it means to be an "unlawful user" or "addicted." Regulations define the terms as including those who have "lost the power of self-control with reference to the use of [a] controlled substance," as well as "current user[s]" of a controlled substance "in a manner other than as prescribed by a licensed physician." The regulations make clear that one need not be using a controlled substance "at the precise time" a firearm is sought so long as use has occurred "recently enough to indicate that the individual is actively engaged in such conduct." Prosecutions and court decisions appear to focus on the term unlawful user , which establishes a lower disability threshold than "addict[]." Cases interpreting the term "typically discuss two concepts: contemporaneousness and regularity," requiring that there be some "pattern" and "recency" of controlled-substance use. For this reason, the prohibition appears to be temporary—that is, one may "regain his right to possess a firearm simply by ending his drug abuse." Prohibition applicable to a person "adjudicated as a mental defective" or "committed to a mental institutio n." The GCA is likewise silent as to the meaning of the terms adjudicated as a mental defective and committed to a mental institution for purposes of that prohibition. The term adjudicated as a mental defective has been interpreted in federal regulations, however, as: (a) A determination by a court, board, commission, or other lawful authority that a person, as a result of marked subnormal intelligence, or mental illness, incompetency, condition, or disease: (1) Is a danger to himself or to others; or (2) Lacks the capacity to manage his own affairs. (b) The term shall include—(1) a finding of insanity by a court in a criminal case, and (2) those persons found incompetent to stand trial or found not guilty by lack of mental responsibility [under the Uniform Code of Military Justice]. Prior to the issuance of the regulatory definition, at least one court had construed the term mental defective narrowly, encompassing only those who have "never possessed a normal degree of intellectual capacity" and excluding persons with "faculties which were originally normal [but which] have been impaired by mental disease." The term committed to a mental institution has also been interpreted in regulations as including a "formal commitment" for "mental defectiveness," mental illness, or "other reasons, such as drug use" by a "court, board, commission, or other lawful authority" that is "involuntary." Whether a person has been formally and involuntarily committed appears to be fact-specific and dependent on state law. Federal law generally does not bar the possession or sale of particular types of firearms, with two major caveats currently in effect. First, the Firearm Protection Owners' Act of 1986 amended the GCA to prohibit the transfer and possession of machineguns. This prohibition does not apply, however, to (1) the transfer to or from, or possession by (or under the authority of) federal or state authorities; and (2) the transfer or possession of a machinegun lawfully possessed before the effective date of the act (May 19, 1986). In response to the 2017 mass shooting in Las Vegas, ATF recently amended the regulatory definition of machinegun for purposes of the NFA and GCA to include bump-stock-type devices, i.e., devices that "allow a shooter of a semiautomatic firearm to initiate a continuous firing cycle with a single pull of the trigger." The amended definition is effective as of March 26, 2019, rendering possession of bump-stock-type devices illegal (subject to exceptions) as of that date pursuant to the machinegun prohibition. Second, the Undetectable Firearms Act of 1988 (UFA) banned the manufacture, importation, possession, transfer, or receipt of firearms that are undetectable by x-ray machines or metal detectors at security checkpoints. The UFA has recently come under renewed scrutiny amid litigation over the dissemination of 3D-printed firearm designs that potentially could undermine the statute's requirements. Though most other types of firearms are lawful, possession of particular firearms may be prohibited based on external factors or the status of the possessor. For instance, it is unlawful to knowingly receive, possess, conceal, store, barter, sell, dispose of, or transport in interstate or foreign commerce any stolen firearm or stolen ammunition. Receipt, possession, and transportation of firearms that have had the importer's or manufacturer's serial number removed or altered are likewise prohibited. Additionally, juveniles—that is, persons under 18 years of age—are barred from knowingly possessing handguns and handgun ammunition, and others may not knowingly transfer such items to them. However, exception is made for, among other things, temporary transfers in the course of employment, ranching or farming activities or for target practice, hunting, or a safety course; possession in the line of duty by juvenile members of the Armed Forces or national guard; transfers of title by inheritance; and possession in defense of the juvenile or another against an intruder into certain residences. Beyond firearms themselves, the GCA prohibits any person from manufacturing or importing armor-piercing ammunition and any manufacturer or importer from selling or delivering such ammunition unless (1) the ammunition is for the use of the U.S. government, a state, or a political subdivision of a state; (2) the ammunition is to be exported; or (3) the ammunition is to be tested or used for experimentation as authorized by the Attorney General. A person who possesses armor-piercing ammunition with a firearm "during and in relation to the commission of a crime of violence or drug trafficking crime" is also subject to separate criminal sentencing provisions. Finally, a person who has been convicted of a felony crime of violence is barred from purchasing, owning, or possessing body armor unless the person has obtained prior written certification from his or her employer that the body armor is needed "for the safe performance of lawful business activity" and the armor's use is limited to the course of such performance. The GCA prohibits the possession of firearms in certain locations. For instance, subject to exceptions, firearms may not be possessed in a "Federal facility," defined as a building (or part of a building) owned or leased by the federal government where federal employees are regularly present for performing their official employment. Additionally, loaded firearms are largely banned on federal land managed by the Army Corps of Engineers with exceptions for law enforcement, certain hunting and fishing activities, use at authorized shooting ranges, and with permission from the district commander. Firearms may generally be carried on most other kinds of federal lands, however, so long as the carrier is not otherwise prohibited by federal law from possessing a firearm and is complying with relevant local firearm laws. The Gun-Free School Zones Act (GFSZA) also amended the GCA to prohibit the knowing possession or discharge of a firearm in a school zone subject to exceptions for law enforcement and possession or discharge on private property not part of school grounds, among other things. As originally enacted, the GFSZA prohibited possession or discharge of any firearm in a school zone. The Supreme Court ruled in United States v. Lopez , however, that such a prohibition exceeded Congress's constitutional authority under the Commerce Clause. In response, Congress amended the statute in 1996 to make clear that it applies only to firearms that have "moved in or that otherwise affect[] interstate or foreign commerce." Though the Supreme Court has not reconsidered the amended GFSZA, lower courts have generally upheld it on the basis of the added textual link to commerce. Several exceptions are set out in 18 U.S.C. § 925 to the firearm possession and transfer restrictions found elsewhere in the GCA. These exceptions primarily relate to firearms intended for the use of federal, state, or local governments or active duty military personnel. But Section 925 also authorizes a person who is barred by the GCA from possessing, transporting, or receiving firearms or ammunition to "make application to the Attorney General for relief" from the disability. The Attorney General has discretion to grant relief if the applicant establishes "to his satisfaction" that relief would not be contrary to the public interest and that the "circumstances regarding the disability, and the applicant's record and reputation, are such that the applicant will not be likely to act in a manner dangerous to public safety." Review of the Attorney General's decision is available in federal district court. This relief-from-disability process has been essentially defunct since 1992, however, as Congress has annually included a provision in ATF appropriations measures prohibiting the expenditure of funds to act on petitions by individuals. Nevertheless, the NICS Improvement Amendments Act of 2007 (NIAA) established, as relevant here, alternative mechanisms for obtaining relief from one of the GCA's firearm disabilities: the disability based on adjudication as a "mental defective" or commitment to a mental institution. Under NIAA, federal departments or agencies making determinations pertinent to that disability—for example, the Department of Veterans Affairs (VA) —must establish programs permitting affected persons to apply for relief. Applications must be acted on within one year, and judicial review is available. Further, the statute encourages states to create similar programs through conditional grants. If an application for relief is granted under one of these programs, the adjudication or commitment "is deemed not to have occurred" for purposes of the GCA, meaning that the firearm prohibition no longer applies. As of December 2017, some three dozen states had enacted qualifying relief programs. The Brady Act requires FFLs—but not private parties who make occasional firearm sales from personal collections or as a hobby—to conduct background checks on prospective firearm purchasers who are not licensed dealers themselves in order to ensure that the purchasers are not prohibited from acquiring firearms under federal or state law. To implement the Brady Act, the FBI created the National Instant Criminal Background Check System (NICS), which launched in 1998. Between the enactment of the Brady Act and the launch of NICS, a set of interim provisions required background checks to be conducted through "the chief law enforcement officer of the place of residence of the transferee," but the Supreme Court struck down those provisions as an unconstitutional usurpation of state executive prerogatives. Today, the NICS background check is completed either by a state "point of contact" (in states that have voluntarily agreed to provide that service) or, otherwise, by the FBI. Through NICS, FFLs can determine whether a prospective firearm purchaser is disqualified from receiving a firearm. NICS is comprised of three FBI-maintained databases The National Crime Information Center Database (NCIC) contains crime data related to persons and property, including persons subject to protective orders, fugitive records, and aliens who have been deported or are deportable because of committing certain crimes. The Interstate Identification Index System (III) contains criminal history information for persons who have been arrested or indicted for any federal or state felony or serious misdemeanor. The NICS Index was created solely for NICS checks and is a catchall index housing records that do not fit under NCIC or III, including mental health and immigration records. Because the three NICS databases rely on record submissions from multiple federal entities and voluntary submissions from individual states, they are not comprehensive catalogues of the records that could identify a person as being prohibited from possessing or purchasing a firearm. As discussed below, Congress has sought on multiple occasions to improve the processes by which records are collected and to make the databases more comprehensive. Generally, the NICS check will quickly tell the dealer whether the sale may or may not proceed, or if it must be delayed for further investigation. If a dealer receives a response that the sale must be delayed, and the NICS check does not further alert the dealer as to whether the prospective purchaser is disqualified within three business days, the sale may proceed at the dealer's discretion. However, the FFL must still verify the transferee's identity by examining a valid identification document. The extent to which NICS examiners continue to investigate delayed requests after the three-day period is unclear, but if an FFL receives a "denied" response after the third day and after the firearm has already been transferred, the FFL "should notify" the NICS Section of ATF that the transfer was completed. An FFL who receives a NICS response denying a transfer will not see the reason for the denial, but the prospective transferee may request the reason from the denying agency (either the FBI or the state or local agency in a point-of-contact state). The denying agency must provide the reason or reasons, in writing, within five business days of receiving the request. Prospective transferees who are denied firearms on the basis of a NICS background check have multiple avenues to challenge the denial. First, the prospective transferee may challenge the accuracy of a record on which the denial was based or assert that his or her right to possess a firearm has been restored by appealing to the denying agency. Second, if that agency cannot resolve the appeal, the prospective transferee may apply for correction of the record directly to the agency that originated the record. If a record is corrected as the result of an appeal, the prospective transferee and relevant agencies are to be notified, and the record is to be corrected in NICS. At this point, the contested firearm transfer may go forward if there are no other disqualifying records, though the FFL will be required to query NICS again if too much time has elapsed since the initial background check. Finally, as an alternative to the agency appeals process, a prospective firearm transferee may contest the accuracy or validity of a disqualifying record in court by bringing an action against the United States or the relevant state or political subdivision, as applicable. Although NICS records of approved firearms transfers containing transferees' identifying information are destroyed within 24 hours, transferees who may be subject to repeated, erroneous denials because of similarities in name or identifying information to prohibited persons may consent to the FBI's retention of their personal information in a "Voluntary Appeal File" for use in preventing "the future erroneous denial or extended delay by the NICS of a firearm transfer." In an attempt to improve access to records concerning persons prohibited from possessing or receiving firearms because of mental illness, restraining orders, and misdemeanor domestic violence convictions, Congress passed the NIAA in early 2008. With respect to federal records, the statute (among other things) imposes a requirement that federal departments and agencies provide information in records pertaining to prohibited persons on a quarterly basis. With respect to state records, NIAA authorizes monetary incentives and penalties tied to submitting records to NICS. First, a state that provides at least 90% of its relevant records is eligible under NIAA for a waiver of a 10% matching requirement connected to an existing state grant program for upgrading criminal history and criminal justice record systems (among other things). To remain eligible for the waiver, a state must biannually certify that at least 90% of records have been made electronically available to the Attorney General. As another incentive, the statute directs the Attorney General to withhold, subject to waiver, up to 5% of funds available from the Edward Byrne Memorial Justice Assistance Grant Program (which provides federal funds for local law enforcement initiatives) if a state provides less than 90% of its available prohibiting records. NIAA also establishes additional grant programs that provide states with money to establish or update information and identification technologies for firearms eligibility determinations, automate record systems, and transmit to NICS the targeted prohibiting records. The recently enacted Fix NICS Act (Fix NICS) aims to further increase federal and state submission of prohibiting records to NICS through additional incentive and accountability measures. At the federal level, departments and agencies must semiannually certify whether they are submitting all prohibiting records on at least a quarterly basis. Federal departments and agencies also must each create an "implementation plan" within one year that is designed to "ensure maximum coordination and automated reporting or making available of records to the Attorney General," and "the verification of the accuracy of those records," with annual benchmarks. The Attorney General is to publish and semiannually submit to Congress the names of departments and agencies that fail to submit the required certification, fail to certify compliance with the reporting obligation, fail to create an implementation plan, or fail to obtain substantial compliance with the implementation plan. Political appointees within a federal department or agency that fail to either certify compliance or substantially comply with an implementation plan will be ineligible for bonus pay. At the state level, Fix NICS reauthorizes some of the grant programs established or utilized by NIAA and ties monetary incentives and preferences under those programs to state creation and substantial compliance with implementation plans like those required of federal departments and agencies. Names of states that do not achieve substantial compliance with their implementation plans are to be published by the Attorney General, while those states determined to be in substantial compliance will receive affirmative preference in Bureau of Justice Assistance discretionary grant applications. The GCA strictly limits the interstate transfer of firearms to non-FFLs. This limitation takes several forms. First, a non-FFL is barred from directly selling or transferring any firearm to any person (other than an FFL) whom the transferor knows or has reason to believe is not a resident of the state in which the transferor resides. Second, FFLs are prohibited from selling or shipping firearms directly to non-FFLs in other states, but FFLs may make in-person, over-the-counter sales of long guns (i.e., shotguns or rifles) to qualified individuals who are out-of-state residents so long as the sales fully comply with the legal conditions of both states. Handguns may be sold only to persons who are residents of the state in which the FFL's premises are located. Non-FFLs who lawfully purchase long guns from out-of-state dealers may transport those firearms back into their states of residence, but such persons are otherwise prohibited from directly transporting into or receiving in their states of residence any firearms purchased or obtained outside the state. Despite the substantial restrictions on interstate firearm sales, federal law ensures that lawful firearm owners may transport their weapons between jurisdictions where it is legal to "possess and carry" them without incurring criminal liability under inconsistent state or local laws so long as the firearms are transported in a specified manner. Current or retired law enforcement officers who meet certain requirements are also entitled to carry concealed firearms throughout the United States regardless of restrictions under state or local law. Violations of many of the prohibitions contained in the GCA and supplementing statutes are punishable as felonies, subjecting violators to criminal fines and statutory imprisonment ranges of varying lengths. Increased penalties are also tied to transporting or receiving firearms in interstate or foreign commerce with intent to use the firearms (or with knowledge they will be used) to commit separate felony crimes, as well as using, carrying, or possessing firearms in connection with "any crime of violence or drug trafficking crime." A person thrice convicted of a "violent felony or a serious drug offense," committed on different occasions, who subsequently possesses or receives a firearm unlawfully is likewise subject to a heightened mandatory minimum sentence of imprisonment. However, the Supreme Court has partially struck down as unconstitutionally vague the definition of the term violent felony , which includes (among other things) any offense involving "conduct that presents a serious potential risk of physical injury to another." In response, past Congresses have considered legislation that would link the heightened penalty instead to prior "serious felony" convictions, with the term serious felony being tied to the authorized or imposed sentence of imprisonment. In a 1986 amendment, FOPA added an explicit mens rea , or intent, requirement to the GCA's penalty provisions. Accordingly, the GCA now imposes its criminal penalties for either knowing or willful violations, depending on the provision. A violation is made knowingly when the person knows the facts that establish the offense. Under this standard, the government need not prove that the defendant knew his behavior was illegal. This is so, according to the Supreme Court, because of the "background presumption that every citizen knows the law," thus making it "unnecessary to adduce specific evidence to prove that 'an evil-meaning mind' directed the 'evil-doing hand.'" Further, to prosecute unlawful possession of a firearm under 18 U.S.C. § 922(g), the federal courts of appeals have consistently concluded that the government must prove only that the defendant knowingly possessed a firearm but not that he had knowledge of the circumstances disqualifying him from possessing a firearm. For example, a prosecutor may prove a knowing violation of 18 U.S.C. § 922(g)(1)—the GCA provision that bars felons from possessing firearms—by establishing only that the defendant knew that he possessed a firearm but not that he knew of his status as a felon at the time he possessed the firearm. However, in January 2019, the Supreme Court granted certiorari in Rehaif v. United States in order to determine whether this interpretation of the GCA is correct or whether the "knowing" requirement must apply to both possession and disqualifying status. Argument in the case is set for April 23, 2019. For willful violations, there is a heightened intent requirement: A violation is willful when the actor knows that the conduct is unlawful. However, for the act to be willful, the actor need not have specific knowledge of provisions of the law he is breaking. Instead, the person must act only "with knowledge that his conduct [is] unlawful." Depending on proof of the requisite mens rea , firearms or ammunition involved in certain violations of the GCA or other federal criminal laws are subject to seizure and forfeiture. Numerous constitutional considerations may inform congressional proposals to modify the current framework for regulating firearms sales and possession. Although Congress has broad constitutional authority to regulate firearms, any firearm measure must be rooted in one of Congress's enumerated powers. In enacting firearms laws, Congress has typically invoked its tax, commerce, and spending powers. Still, when exercising those enumerated powers, Congress must be mindful of other constitutional restraints, such as those flowing from the Second Amendment, the Fifth Amendment's Due Process Clause, and principles of federalism. This section provides an overview of the primary powers Congress has invoked to enact firearms measures and then addresses the constitutional constraints that independently could limit Congress's ability to regulate firearms. Article I of the Constitution, which enumerates powers of Congress, declares that "[t]he Congress shall have Power To lay and collect Taxes." This broad power enables Congress to tax many activities that it could not directly regulate. Still, "[e]very tax is in some measure regulatory" by creating "an economic impediment to the activity taxed as compared with others not taxed." Because a tax can shape behavior, when imposing a tax Congress may be motivated by an objective other than raising revenue, like limiting the supply of certain firearms. And provisions of a tax measure that go beyond the actual collection of the tax, such as penalty provisions, are considered lawful so long as they are reasonably related to the exercise of Congress's tax power and not "extraneous to any tax need." Congress's tax power is not without limitation, however. While the Supreme Court often will "decline[] to closely examine the regulatory motive or effect of revenue-raising measures," the Court has indicated that it will step in when a tax measure is "so punitive" that it "loses its character as [a tax] and becomes a mere penalty with the characteristics of regulation and punishment." Congress invoked its tax power when enacting the NFA. Within a few years of its enactment, in 1937, the Supreme Court upheld the NFA as a lawful exercise of Congress's tax power in Sonzinsky v. United States . Notwithstanding the NFA's deterrent purpose, the Court opined that "a tax is not any the less a tax because it has a regulatory affect." The Court further concluded that the NFA's registration requirements were "obviously supportable as in aid of a revenue purpose," and, the Court added, the tax produced "some revenue." More recently, in 2018 the Tenth Circuit, relying on Sonzinsky , upheld the NFA's taxing and registration scheme as a valid exercise of Congress's tax power in a challenge to the NFA's regulation of firearm silencers. The Tenth Circuit rejected the defendants' argument that the NFA, in modern times, is "far more of a gun- control measure than a gun- tax measure." The defendants had principally argued that, because the NFA taxes collect no net revenue, "the NFA's taxing purpose disappear[ed], leaving only its regulatory effect," thus rendering the tax unconstitutional. But the Tenth Circuit declined to create a heightened constitutional requirement for Congress's tax power that would require a tax to produce net revenue, pointing to the Supreme Court's continued emphasis, since Sonzinsky , on whether a tax measure collects "some" gross revenue, no matter how small. The Constitution grants Congress the power "to regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." The Commerce Clause, as interpreted by the Supreme Court, authorizes Congress to regulate three categories of activities related to interstate commerce: (1) "channels" of interstate commerce, like highways and hotels; (2) "instrumentalities of interstate commerce, or persons or things in interstate commerce," such as motor vehicles and goods that are shipped; and (3) "activities that substantially affect interstate commerce," which include intrastate activities (such as robbery) "that might, through repetition elsewhere," substantially affect interstate commerce. Congress has relied on the Commerce Clause as a constitutional basis for GCA provisions restricting the manufacture, import, sale, transfer, and possession of firearms, and the Supreme Court has reviewed a number of these regulations. Early cases mainly involved statutory interpretation, centering on what conduct the statutory prohibitions reached. Only the most recent case— United States v. Lopez —directly addressed the scope of Congress's Commerce Clause power to regulate firearms. For example, in the 1971 ruling United States v. Bass , the Supreme Court analyzed the scope of a law enacted as part of Title VII of the Omnibus Crime Control and Safe Streets Act of 1968, which made it a federal crime for a felon to "receive[], possess[], or transport[] in commerce o r affecting commerce ... any firearm." (A similar provision is found in the current version of the GCA. ) In Bass , the Court held that the language "in commerce or affecting commerce" applied to all three listed activities—receiving, possessing, and transporting—and not just the last one. In resolving the textual ambiguity this way, the Court in part relied on federalism principles (discussed in more detail infra ), reasoning that if the statute had reached "mere possession," wholly untethered to interstate commerce, the provision would have "dramatically intrud[ed] upon traditional state criminal jurisdiction." In light of the Court's interpretation of the statute, it declined to opine on whether the Commerce Clause could provide a basis for Congress to regulate the "mere possession" of a firearm. A few years later, in Scarborough v. United States , the Supreme Court reviewed the same provision to determine when the firearm must travel in interstate commerce for the possession ban to apply to felons. The Court ultimately concluded that the criminal provision applied to any felon who possessed a firearm that had "at some time" traveled in interstate commerce. In rejecting the defendant's contention that the possession itself must be contemporaneous with interstate commerce, the Court pointed to contrary legislative intent. In particular, the Court concluded that the legislative history "supports the view that Congress sought to rule broadly to keep guns out of the hands of those who have demonstrated that 'they may not be trusted to possess a firearm without becoming a threat to society,'" without "any concern with either the movement of the gun or the possessor or with the time of acquisition." Similarly, in Barrett v. United States , the Supreme Court analyzed the scope of the interstate commerce nexus in a GCA provision that made it unlawful for certain categories of persons, such as felons, "to receive any firearm or ammunition which has been shipped or transported in interstate or foreign commerce." The Court concluded that the term to receive applies to the intrastate acquisition of a firearm if that firearm previously had been transported in interstate commerce (e.g., from the manufacturer to the distributor to the dealer). The Court reasoned that the language "has been" shipped or transported in interstate commerce "denot[es] an act that has been completed" and thus applies "to a firearm that already has completed its interstate journey and has come to rest in the dealer's showcase at the time of its purchase and receipt by the felon." Finally, the Court commented that interpreting the provision to apply only to interstate receipts "would remove from the statute the most usual transaction, namely, the felon's purchase or receipt from his local dealer," and that interpretation, in the Court's view, would contravene Congress's "concern with keeping firearms out of the hands of categories of potentially irresponsible persons." Most recently, in its 1995 opinion United States v. Lopez , the Supreme Court reviewed—and invalidated—the GFSZA, which criminalized the possession of a firearm in a school zone but contained no explicit nexus to interstate commerce. The government had argued that firearm possession in a school zone may cause violent crime, which could affect the national economy by (1) handicapping the educational process, which would generate a "less productive citizenry," and (2) spawning substantial financial losses "spread throughout the population" through insurance costs and the "reduce[d] willingness of individuals to travel to areas within the country that are perceived to be unsafe." The Court rejected these arguments, opining that if the Commerce Clause could reach such activity, it essentially would authorize a federal police power, a constitutional power the Framers declined to give to the federal government. Without finding a substantial effect on interstate commerce, the Court further concluded that the law exceeded Congress's power under the Commerce Clause because "[t]he Act neither regulate[d] a commercial activity nor contain[ed] a requirement that the possession be connected in any way to interstate commerce." Congress subsequently amended the provision to provide expressly that, for the possession of a firearm in a school zone to be a federal crime, the government must show that the firearm "moved in or ... otherwise affects interstate or foreign commerce." This amended version of the statute has been upheld by lower courts against constitutional challenges. Article I grants Congress broad authority to enact legislation for the "general welfare" through its spending power. When invoking this power, Congress can place conditions on funds distributed to the states that require those accepting the funds to take certain actions that Congress otherwise could not directly compel the states to perform. Still, the Supreme Court has articulated several limitations on Congress's power to attach conditions to the receipt of federal funds—namely, any condition must be written unambiguously, so that state lawmakers understand the full consequences of accepting or declining funds; must be germane to the federal interest in the particular program to which the money is directed; cannot induce the recipient states to engage in an activity that would independently violate the Constitution; and cannot be "so coercive as to pass the point at which pressure turns into compulsion." Arguably, the most difficult limitation to glean is whether a spending condition is unduly coercive. Two Supreme Court opinions exploring the bounds within which Congress must stay offer some guidance. First, in South Dakota v. Dole , the Supreme Court upheld a 1984 congressional measure designed to encourage states to raise the minimum drinking age to 21. To achieve this result, Congress directed the Secretary of Transportation to withhold 5% of certain federal highway grant funds from states with a lower minimum drinking age. In upholding the spending condition, the Court concluded that a state stood to lose only "a relatively small percentage of certain federal highway funds," which the Court further described as "relatively mild encouragement." Second, and more recently, in National Federation of Independent Business v. Sebelius ( NFIB ), the Supreme Court struck down a provision of the Patient Protection and Affordable Care Act of 2010 (ACA) that purported to withhold Medicaid funding from states that did not expand their Medicaid programs. Unlike in Dole , in NFIB the Court concluded that the financial condition placed on the states in the ACA (withholding all federal Medicaid funding, which, according to the Court, typically totals about 20% of a state's entire budget) was akin to "a gun to the head" and thus unlawfully coercive. The Second Amendment states that "[a] well-regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear arms, shall not be infringed." In District of Columbia v. Heller , the Supreme Court held that the Second Amendment guarantees an individual right to possess firearms for historically lawful purposes. Since Heller , the Supreme Court has substantively opined on the Second Amendment one other time, holding in McDonald v. City of Chicago that the Second Amendment right is incorporated through the Fourteenth Amendment to apply to the states. During the upcoming October 2019 term, the Supreme Court is scheduled to review a Second Amendment challenge to a New York City firearm licensing provision in New York Rifle & Pistol Association v. City of New York . That ruling may provide further guidance for Congress in crafting legislation that comports with the Second Amendment. In Heller the Supreme Court did not elaborate on the full extent of the Second Amendment right. But a number of takeaways may be distilled from the Court's opinion. First, the Court concluded that the Second Amendment codified a pre-existing individual right to keep and bear arms for lawful purposes, such as self-defense and hunting, unrelated to militia activities. Second, the Court singled out the handgun as the weapon that "the American people have considered ... to be the quintessential self-defense weapon." But the Court clarified that, "[l]ike most rights, the right secured by the Second Amendment is not unlimited" and further announced that "nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of firearms," among other "presumptively lawful" regulations. Additionally, as for the kind of weapons that may obtain Second Amendment protection, the Court opined that the Second Amendment's coverage is limited to weapons "in common use at the time" that the reviewing court is examining a particular firearm; the conclusion, the Court added, "is fairly supported by the historical tradition of prohibiting the carrying of dangerous and unusual weapons." Since Heller , the circuit courts have largely been applying a two-step inquiry, drawn from the discussion in Heller , to determine whether a particular law is constitutional. First, courts ask whether the challenged law burdens conduct protected by the Second Amendment. If so, courts next ask whether, under some type of means-end scrutiny, the law is constitutional under that standard of review. To date, no federal appellate court has invalidated on Second Amendment grounds any provision of the GCA or NFA. Nonetheless, when considering proposals to expand federal firearm restrictions, Congress may want to consider whether the expansion would fit within the parameters established in Heller and subsequent jurisprudence as permissible under the Second Amendment. The Due Process Clause of the Fifth Amendment provides that "[n]o person shall be ... deprived of life, liberty, or property, without due process of law." "The touchstone of due process is protection of the individual against arbitrary action of government." The Due Process Clause has a substantive and procedural component, described below, and may become relevant in the context on firearms regulation if the government deprives a person of constitutionally protected liberty interest (e.g., a right to keep and bear arms under the Second Amendment) or property interest (e.g., a firearm license). The substantive component of the Due Process Clause prohibits "the exercise of power without any reasonable justification in the service of a legitimate governmental objective." As relevant here, a substantive due process violation may occur when a legislative measure infringes on a fundamental right. But "[w]here a particular [constitutional] Amendment provides an explicit textual source of constitutional protection against a particular sort of government behavior," like the Second Amendment, "that Amendment, not the more generalized notion of 'substantive due process,' must be the guide for analyzing" such claims. Accordingly, it appears that in the event the government deprives a person of the right to keep and bear arms—the potential result of an overly stringent federal firearms measure—the touchtone of a reviewing court's constitutional analysis would be the Second Amendment rather than the substantive component of the Due Process Clause. Still, the Due Process Clause also requires that the government afford persons with adequate procedures when depriving them of a constitutionally protected interest. This "[p]rocedural due process imposes constraints on governmental decisions which deprive individuals of 'liberty' or 'property' interests within the meaning of the Due Process Clause of the Fifth ... Amendment." Examining procedural due process involves a two-step inquiry. First, a court asks whether the government has interfered with a protected liberty or property interest. In the context of federal firearms regulations, at least two constitutionally protected interests could be affected: (1) the fundamental liberty interest in a person's right to keep and bear arms, granted by the Second Amendment (i.e., the right to purchase and possess firearms for lawful purposes), and (2) the property interest in a government-issued firearms license (e.g., if the person is an FFL whose license is revoked by the government). If the government has deprived a person of one of these constitutionally protected interests, courts ask, second, whether the government, in deciding whether to make the deprivation, used constitutionally sufficient procedures. Adequate due process generally requires notice of the deprivation and an opportunity to be heard before a neutral party. This constitutional requirement, the Supreme Court says, is meant to be "flexible and calls for such procedural protections as the particular situation demands." Accordingly, the appropriate process due—i.e., the type of notice, the manner and time of a hearing regarding the deprivation, and the identity of the decisionmaker—will vary based on the specific circumstances at hand. To determine what procedures should be applied to a deprivation of a constitutionally protected interest, courts apply the balancing test outlined in Mathews v. Eldridge. This test requires courts to weigh three factors: (1) the private interest affected; (2) the risk of an erroneous deprivation of that interest through the procedures used; and (3) the government's interest. Accordingly, although substantive due process concerns surrounding firearms measures may fuse with the Second Amendment concerns identified above, the procedural component of the Due Process Clause raises independent considerations for Congress. For instance, procedural due process may be relevant to congressional consideration of firearm measures that may result in the revocation or inability to obtain a license to own, purchase, or sell a firearm. Accordingly, when considering a firearms licensing measure, Congress may want to keep in mind the standards and procedures for obtaining and revoking such a license to ensure that due process is supplied. The Constitution establishes a system of dual sovereignty in which "both the National and State Government have elements of sovereignty the other is bound to respect." For instance, the Constitution explicitly grants certain legislative powers to Congress in Article I and then reserves all other legislative powers for the states to exercise. Both the federal government and the states regulate firearms, and two federalism principles particularly inform this shared policymaking role: the preemption and anti-commandeering doctrines. The preemption doctrine derives from the Constitution's Supremacy Clause, which declares that "the Laws of the United States ... shall be the supreme Law of the Land." Congress, through legislation lawfully enacted pursuant to an independent source of constitutional authority, may "preempt" (i.e., invalidate) state law. The Supreme Court has articulated that the doctrine operates as follows: "Congress enacts a law that imposes restrictions or confers rights on private actors; a state law confers or imposes restrictions that conflict with the federal law; and therefore the federal law takes precedence and the state law is preempted." In other words, whenever states and the federal government regulate in the same area, like firearms, and the state and federal measures conflict, the conflict is to be resolved in favor of the federal government. Notwithstanding the supremacy of federal law, the anti-commandeering doctrine bars the federal government from directly regulating the states. The doctrine is "the expression of a fundamental structural decision incorporated into the Constitution" to limit Congress's authority, including "to withhold from Congress the power to issue orders directly to the States." Accordingly, Congress cannot direct the states to enact a particular measure, nor can it conscript state employees, or those of its political subdivisions, to enforce a federal regulatory program. Similarly, the federal government cannot prohibit a state from enacting new laws. As a result, the federal government cannot require the states to enforce a particular federal firearm regulatory regime. In Printz v. United States , for example, the Supreme Court struck down under the anti-commandeering doctrine certain interim provisions of the Brady Act. The relevant provisions required state and local law enforcement officers to conduct background checks on prospective handgun purchasers. The Court held that a federal mandate requiring state and local law enforcement to perform background checks on prospective handgun purchasers violated constitutional principles of federalism "by conscripting the State's officers directly" to enforce a federal regulatory scheme. Federal firearms regulation has been a subject of continuous interest for Congress. A range of proposals have been in this and past Congresses. Some seek to ease federal firearms restrictions or facilitate state reciprocity in the treatment of persons authorized to carry firearms by another state; others seek greater restrictions on the federal laws concerning the possession, transfer, or sale of firearms or the expansion of background checks for firearm purchases. These various approaches, in turn, prompt various constitutional questions, including Congress's constitutional authority to legislate on such matters and whether the proposed measures comport with the Second Amendment and other constitutional constraints. This section discusses several congressional proposals related to 3D-printed firearms, background checks, mental illness, particular firearms and accessories (e.g., semiautomatic assault weapons, bump stocks, silencers), and "red flag" laws and identifies related constitutional questions. Under the Undetectable Firearms Act of 1988 (UFA), it is unlawful for any person to manufacture, import, sell, ship, deliver, possess, transfer, or receive a firearm (1) that, after removal of grips, stocks, and magazines, is not detectable by walk-through metal detectors; or (2) any major component of which does not generate an accurate image when scanned by the types of x-ray machines commonly used at airports. These prohibitions grew out of a concern that the increasing use of lightweight, noncorrosive plastics as a substitute for metal in firearm-component manufacturing would lead to the proliferation of firearms not detectable at security checkpoints. Despite the prohibitions in the UFA, the advent of 3D-printing technology and its application to firearms has prompted concern about a new wave of undetectable, plastic guns that technically comply with the statute and could fall into the wrong hands. A high-profile example of a design for such a gun is the "Liberator" pistol, plans for which were first disseminated in 2013 by Defense Distributed—a nonprofit "private defense firm" and FFL. According to media reports, the design for the Liberator allows for the 3D-printing of a functioning pistol that is almost entirely plastic, with the only metal components being a small firing pin and a removable piece of steel that is included specifically to make the design compliant with the UFA. In other words, the irrelevance of the steel block to the firearm's functionality potentially could allow bad actors to produce operable and concealable plastic firearms that would not be caught by metal detectors. With respect to Defense Distributed specifically, years of litigation over the company's online dissemination of computer files for 3D-printed nonmetallic firearms has mostly stymied the company's efforts to share its files on the internet. Most recently, a federal district court in Washington entered an order that effectively bars Defense Distributed from making its disputed files available online for the duration of the ongoing lawsuit in that jurisdiction. Nevertheless, the company's continuing efforts to spread its designs for nonmetallic firearms have raised novel constitutional questions without easy answers, including (1) whether First Amendment free speech protections extend to computer code (which could bring Defense Distributed's activities within the amendment's scope), and (2) whether the Second Amendment protects the right to make arms as a necessary precursor to keeping and bearing them. Faced with the long-simmering dispute over dissemination of 3D-printed gun files and the possibly incomplete protections of the UFA, the 115 th and 116 th Congresses have considered legislation addressing the online spread of 3D-printed gun files and the possession of 3D-printed guns themselves. For instance, the 3D-Printed Gun Safety Act of 2018 would have made it unlawful to "intentionally publish" on the internet "digital instructions ... that can automatically program" a 3D printer or similar device to produce or complete a firearm. Perhaps with First Amendment concerns in mind, the bill's "Findings" section stated that Congress's intention was not "to regulate the rights of computer programmers" but was instead "to curb the pernicious effects of untraceable—and potentially undetectable—firearms." Other legislation would appear to have banned firearm assembly kits or firearm components that might be produced with a 3D printer either by amending the definition of firearm in the GCA or by bringing such items within the purview of the Consumer Product Safety Act. The Untraceable Firearms Act of 2018 additionally would have expanded serial number requirements, extended the UFA to firearms lacking detectable major components, and clarified that manufacturing firearms under the GCA includes 3D printing, among other things. Finally, a bill introduced in the 115 th Congress would have amended the GCA to prohibit the manufacture of firearms or components by means of a 3D printer and the transfer or possession of any such items. The 116 th Congress began with a push in the House to expand firearm background checks. Two House bills were passed in February 2019: (1) H.R. 8, the Bipartisan Background Checks Act of 2019, and (2) H.R. 1112 , the Enhanced Background Checks Act of 2019. If enacted, H.R. 8 would expand background checks to capture many private transfers between non-FFLs, subject to enumerated exceptions. (A similar bill has been introduced in the Senate. ) One question the bill raises is whether it may be lawfully enacted under one of Congress's Article I powers. The bill's accompanying constitutional authority statement does not specify which Article I power Congress is invoking to enact the measure, but the bill may be an attempt to exercise Congress's commerce power. Although the bill does not use the word commerce , other GCA provisions lack an explicit textual hook to the Commerce Clause. Courts reviewing other federal firearms law without a textual hook have upheld those measures after distinguishing them from the firearm possession law struck down in Lopez . Accordingly, the constitutionality of H.R. 8, as a lawful enactment under the Commerce Clause, may depend on the ability to distinguish it from the flaws the Supreme Court identified in Lopez . H.R. 1112 would amend the so-called "default proceed" process that allows an FFL to transfer a firearm when the NICS check has not been completed within three business days. The bill provides a mechanism for a transfer to occur if the FFL does not receive instructions from the NICS system on whether to proceed with or deny a proposed transaction within 10 business days. If the transferee wishes to proceed with the sale in such cases, he or she must file a petition (electronically or via first-class mail) to the Attorney General certifying that the transferee does not believe he or she is prohibited from acquiring the firearm. If a response is not provided within 10 business days, the FFL would be allowed to proceed with the transfer. The committee report accompanying the bill appears to construe these 10-day periods as occurring in succession rather than concurrently (i.e., the delay period might last up to 20 business days). Because the bill potentially could delay a sale to a law-abiding citizen up to 20 business days, there may be questions about whether those persons have received adequate procedural due process in the short-term deprivation of a constitutionally protected interest. Because the temporary deprivation (i.e., the inability to purchase a firearm for self-defense) would occur before a firearm may be transferred to the prospective purchaser, a reviewing court would be tasked with determining whether post-deprivation proceedings—meaning proceedings that take place after a person has been deprived of a constitutionally protected interest—are constitutionally permissible. Typically, due process requires that a person be given an opportunity to be heard before the deprivation of a protected interest may occur; in that case there are pre-deprivation hearings. But the Supreme Court has recognized in circumstances in which the government "must act quickly, or where it would be impractical to provide pre-deprivation process, post-deprivation process satisfies the requirements of the Due Process Clause." Some Members of Congress have proposed measures that would require states to recognize concealed carry privileges afforded by other states. Both S. 69, the Constitutional Carry Reciprocity Act of 2019, and H.R. 38 , the Concealed Carry Reciprocity Act of 2019, if enacted, would allow persons who are eligible to carry a concealed handgun in one state to lawfully carry a handgun in other states that have a concealed-carry regime for their residents without regard to differences in the states' eligibility requirements for concealed carry. Both bills purport to preempt state laws to varying degrees. Whether these preemption provisions are considered to be valid likely will depend on whether the bills, as a whole, are interpreted to "confer[] on private entities ... a federal right to engage in certain conduct," i.e., carrying a concealed handgun, "subject only to certain (federal) constraints." H.R. 38 also contains a civil-suit provision that would authorize a private right of action against any person, state, or local government entity that interferes with a concealed-carry right that the bill establishes. Because the bill seeks to abrogate the states' Eleventh Amendment immunity from suit in federal court, several questions need to be answered, the first being what exception to Eleventh Amendment immunity the bill is invoking. Given that the bill cites the Second Amendment as the constitutional source of authority, it is possible that the bill seeks to invoke Congress's enforcement power under Section Five of the Fourteenth Amendment. Section Five of the Fourteenth Amendment enables Congress to abrogate a state's Eleventh Amendment immunity through legislation designed to enforce the Fourteenth Amendment's protections. And the Second Amendment is made enforceable on the states via the Fourteenth Amendment. If Congress, indeed, intends to invoke its Section Five power, a second question raised is whether legislation designed to remedy or deter state violations of the Second Amendment would be a permissible exercise of Congress's Section Five enforcement power. And assuming that Congress could lawfully exercise its Section Five power to enforce violations of Second Amendment rights, a third question would be whether the Second Amendment protects the right to carry a concealed handgun—an issue that has divided the federal appellate courts. As described previously, a person who has been "adjudicated as a mental defective" or "committed to a mental institution" is barred by federal law from transporting, possessing, or receiving firearms or ammunition. Both regulatory and judicial interpretations of these terms have focused on the need for a formal decision by an authoritative body like a court or board after an adjudicative hearing, as broader interpretations could raise constitutional due process and Second Amendment concerns. Nevertheless, the prohibition—even construed narrowly—has been criticized in some quarters as unconstitutional given its effectively permanent nature or as stigmatizing mental illness and unfairly painting as dangerous individuals who are more likely to be victims than perpetrators of violent crime. At the same time, some observers have, in response to past mass shootings, called for even stricter limits on possession of firearms by the mentally ill. For its part, the 115 th Congress considered bills that would have both broadened and narrowed the existing firearm prohibition. Some legislation would have, among other things, adopted the narrow understanding that an adjudication or commitment for purposes of the firearm prohibition must stem from an order or finding of an "adjudicative body" after a hearing and that the order or finding may impose only a temporary disability. Other legislation would have added temporary firearm prohibitions for persons assessed by mental health professionals to pose a risk of danger to others. Apart from constitutional and interpretive issues, commentators have highlighted the challenges of collecting comprehensive mental health records for use in NICS background checks, contending that the 2007 Virginia Tech shooting could have been avoided if the gunman's prior state mental health adjudication had been reported. One challenge specific to collecting mental health records is that many such records are held by state or local agencies that may believe patient information must remain confidential pursuant to the Health Insurance Portability and Accountability Act (HIPAA). To combat this perception, the Department of Health and Human Services issued a rule in 2016 that expressly allows specified state entities to report limited information otherwise covered by HIPAA to NICS or to another entity that reports to NICS. As noted above, Congress has also sought to improve mental health record reporting at the state level through NIAA, which (among other things) funds state efforts to develop systems for accurate and complete reporting. NICS reporting of mental health records at the federal level has raised somewhat different issues. Although federal agencies are generally required to report mental health adjudication records for background check purposes, NIAA makes clear that federal departments and agencies may not furnish such records if the relevant adjudication has been set aside or the person has been found to be "rehabilitated," among other things. Additionally, the Department of Veterans Affairs (VA), which appears to supply the vast majority of federal mental health records to NICS, has for years provided records of beneficiaries who are appointed fiduciaries to manage their financial affairs based on a VA determination that the beneficiaries are "mentally incompetent"; concern that this practice may unfairly deprive veterans of their right to possess firearms, however, led to the introduction of legislation in the 115 th Congress that would have ensured that veterans for whom fiduciaries are appointed are not considered "adjudicated as a mental defective" unless a judicial authority has issued an order or finding "that such person is a danger to himself or herself or others." A final rule published by the Social Security Administration (SSA) in December 2016, which specified similar conditions for SSA reporting of disability program beneficiaries who were appointed a representative payee, was also vacated by Congress through a Congressional Review Act resolution early in 2017. Numerous proposals have been made over the years to limit or expand the ability to possess certain kinds of firearms and accessories. For example, bills have targeted limiting the possession of semiautomatic "assault weapons," large-capacity ammunition feeding devices, and bump stocks. Conversely, other bills have proposed decreasing regulations on firearm silencers. There has been continued interest in tightening the regulation of semiautomatic "assault weapons" since the 1994 ban expired in 2004. Some proposals seek to reinstate and expand upon the former assault weapon ban. Congress has also considered bringing certain semiautomatic firearms under the more-stringent NFA's regulatory scheme. Further, some Members of Congress have proposed to make it unlawful for an FFL to sell or transfer to any person under 21 years old certain semiautomatic rifles; currently, anyone age 18 or older may purchase such rifles from an FFL. Banning the possession of these kinds of firearms entirely or by a subset of the population may raise Second Amendment questions, such as the extent to which the Second Amendment protects the right of all persons to bear specific arms other than handguns in the home for self-defense. To date every federal appellate court that has reviewed a state or local semiautomatic assault weapon ban has rejected Second Amendment challenges to those laws. Nor has a federal appellate court sustained a challenge to the current federal law that prohibits the sale of handguns to persons under 21 years old. There have also been proposals to ban "bump stock" devices, which can be attached to a semiautomatic firearm and allow it to effectively mimic the firing capability of a fully automatic weapon. After it was discovered that the assailant behind the Las Vegas, Nevada, mass shooting in October 2017 used one of these firearm accessories, ATF initiated the process of regulating them. ATF published a final rule the next year, on December 26, 2018, banning the transfer and possession of all bump stock devices, effective March 26, 2019. Litigation seeking to enjoin the rule before its effective date followed. The plaintiffs challenged the rulemaking process and the rule itself. Codifying the ban through legislation would avoid the challenges to the rulemaking process but could potentially be subject to constitutional challenge under the Takings Clause, which forbids "private property [to] be taken for public use, without just compensation." In this vein, takings lawsuits for compensation under the Tucker Act or Little Tucker Act potentially could be brought by persons who owned bump stock devices before the effective date of any statutory ban. Still, these constitutional concerns could be alleviated by creating a grandfather clause for bump stocks that were lawfully owned before the effective date of any bump stock ban. Additionally, there have been congressional efforts to deregulate firearm silencers, which are currently regulated under the NFA and GCA. In the SHUSH Acts, as introduced in the House and Senate, some Members have proposed measures that, if enacted, would eliminate the federal regulation of firearm silencers entirely. These bills also seek to preempt state and local laws that impose a tax on the making, transferring, possessing, or transporting of a firearm silencer as well as those that require marking, recordkeeping, or registering the same. Less expansive proposals purport only to remove silencers from NFA regulation. Thus, if the bills were enacted, silencers would not be subject to the NFA's tax and registration requirements but would still be subject to all GCA firearm regulations. Still, this proposal contains the same preemption provisions as the more comprehensive SHUSH Acts. All three bills may raise questions about whether the preemption provisions are constitutionally valid, as Congress can only preempt state and local measures when those measures conflict with a federal regulation covering the same activity. As relevant here, though, Congress, as part of a deregulation measure, may expressly prohibit states from further regulating the same activity "[t]o ensure that the States would not undo federal deregulation with regulation of their own." Somewhat related to mental health firearm restrictions are proposals for so-called "red flag" laws, which generally permit courts to issue temporary orders barring particular persons from possessing guns based on some showing of imminent danger or a risk of misuse. Following the February 2018 school shooting in Parkland, Florida, a number of states proposed or passed red-flag laws, and legislation has been introduced in the 116 th Congress on the subject. Disagreement over various proposals has largely turned on the stringency of the showing that must be made to obtain an order, the persons who may seek an order, whether an initial order may be obtained without the presence of the gun owner, and the length of the resultant firearm disability. Red-flag legislation may raise questions as to whether such measures run afoul of the Second Amendment and deprive gun owners (or prospective gun owners) of constitutionally protected interests without due process of law. However, proponents of such laws assert that they are an effective and needed means of averting gun violence before it happens and that hearing and review procedures are constitutionally adequate. Were a court to consider a constitutional challenge to a red-flag measure under the Second Amendment or Due Process Clause, the outcome potentially could depend on (1) the court's conception of the scope of the right to keep and bear arms in light of Heller and (2) the weight ascribed by the court to the three Mathews v. Eldridge factors based on the particular procedures of the measure at issue.

Summary: Firearms regulation is an area of shared authority among federal, state, and local governments. Individual states have enacted a diverse range of laws relating to the possession, registration, and carrying of firearms, among other things. Federal law establishes a regulatory framework for the lawful manufacture, sale, and possession of firearms at the national level. The federal framework generally serves as a floor for permissible firearm use and transactions, leaving states free to supplement with additional restrictions so long as they do not conflict with federal law. Federal laws regulating firearms date back roughly a century, and over time lawmakers have established more stringent requirements for the transfer, possession, and transportation of firearms. The two principal federal firearms laws currently in force are the National Firearms Act of 1934 (NFA) and the Gun Control Act of 1968 (GCA), as amended. The NFA was the first major piece of federal legislation regulating the sale and possession of firearms. Through a taxation and registration scheme, the law sought to curb the rise of violence connected to organized crime by targeting the types of weapons that (at the time of passage) were commonly used by gang members. Congress passed the GCA in the wake of the assassinations of Dr. Martin Luther King Jr. and Senator Robert Kennedy to prevent firearm possession by prohibited persons and to help law enforcement stem increasing crime rates. The GCA is a complex statutory regime that has been supplemented regularly in the decades since its inception. Broadly speaking, the GCA, as amended, regulates the manufacture, transfer, and possession of firearms, extending to categories of weapons that fall outside the scope of the NFA. In general terms, the GCA sets forth who can—and cannot—sell, purchase, and possess firearms, how those sales and purchases may lawfully take place, what firearms may lawfully be possessed, and where firearm possession may be restricted. The Brady Handgun Violence Prevention Act amended the GCA to require a background check for many, but not all, firearms transfers. Numerous constitutional considerations may inform congressional proposals to modify the current framework for regulating firearms sales and possession. Although Congress has broad constitutional authority to regulate firearms, any firearm measure must be rooted in one of Congress's enumerated powers. In enacting firearms laws, Congress has typically invoked its tax, commerce, and spending powers. For example, the NFA invokes Congress's tax power, and many GCA provisions invoke Congress's commerce power. Additionally, Congress has used its spending power to incentivize states, through offering grant money, to provide comprehensive records to the FBI's National Instant Background Check System (NICS). When exercising its enumerated powers, Congress nevertheless must be mindful of other constitutional restraints. Congress may want to look to the Supreme Court's Second Amendment jurisprudence—chiefly, District of Columbia v. Heller—when imposing any firearm restriction. In Heller, the Supreme Court held that the Second Amendment provides an individual right to keep and bear arms for lawful purposes. Further, the Due Process Clause of the Fifth Amendment limits Congress's ability to deprive a person of any constitutionally protected interest, such as Second Amendment firearms rights, and rights in property, such as firearms and accessories. Moreover, when enacting measures seeking to limit state firearm schemes, Congress may want to consider the federalism limits inherent in the Constitution's system of dual sovereignty, such as the anti-commandeering doctrine. These constitutional considerations are relevant to the scope of legislation that the 115th and 116th Congresses have considered to amend the existing federal statutory framework of firearms regulation. Among other things, such legislation has focused on issues arising from the dissemination of 3D-printed and untraceable firearms, gaps in the collection of records for background checks of prospective firearm purchasers, restrictions on certain types of firearms and accessories, possession of firearms by the mentally ill, interstate reciprocity for lawful concealed carry of firearms, and laws permitting courts to order that firearms be temporarily removed from persons deemed to be a risk to themselves or others.