Federal law punishes convicted sex offenders for failure to register or to update their registration as the Sex Offender Registration and Notification Act (SORNA) demands. The offense consists of three elements: (1) a continuing obligation to report to the authorities in any jurisdiction in which the individual resides, works, or attends school; (2) the knowing failure to comply with registration requirements; and (3) a jurisdictional element, i.e ., (a) an obligation to register as a consequence of a prior qualifying federal conviction or (b)(i) travel in interstate or foreign commerce, (ii) travel into or out of Indian country, or (iii) residence in Indian country. Violators face imprisonment for not more than 10 years. The registration offense carries an additional penalty of imprisonment for not more than 30 years, but not less than 5 years, if the offender is also guilty of a federal crime of violence. The Adam Walsh Child Protection and Safety Act created SORNA. SORNA revised an earlier nationwide sex offender registration system, the Jacob Wetterling Act. The Jacob Wetterling Act encouraged the states to establish and maintain a registration system. Each of them had done so. Their efforts, however, though often consistent, were hardly uniform. The Walsh Act preserves the basic structure of the Wetterling Act, expands upon it, and makes more specific matters that were previously left to individual state choice. The Walsh Act contemplates a nationwide, state-based, publicly available, contemporaneously accurate, online system. Jurisdictions that fail to meet the Walsh Act's threshold requirements face the loss of a portion of their federal criminal justice assistance grants. The Walsh Act vests the Attorney General with authority to determine the extent to which SORNA would apply to those with qualifying convictions committed prior to enactment. After enactment, the Attorney General promulgated implementing regulations that imposed the registration requirements on those with pre-enactment convictions. Conscious of the legal and technical adjustments required of the states, the Walsh Act afforded jurisdictions an extension to make the initial modifications necessary to bring their systems into compliance. Thereafter, states not yet in compliance have been allowed to use the penalty portion of their federal justice assistance funds for that purpose. The Justice Department indicates that 17 states, 3 territories, and numerous tribes are now in substantial compliance with the 2006 legislation. Section 2250 convictions require the government to prove (1) that the defendant had an obligation under SORNA to register and to maintain the currency of his registration information; (2) that the defendant knowingly failed to comply; and (3) that one of the section's jurisdictional prerequisites has been satisfied. SORNA directs anyone previously convicted of a federal, state, local, tribal, or foreign qualifying offense to register and to keep his registration information current in each jurisdiction in which he resides or is an employee or student. Initially, he must also register in the jurisdiction in which he was convicted if it is not his residence. Registrants who relocate or who change their names, jobs, or schools have three business days to appear and update their registration in at least one of the jurisdictions in which they reside, work, or attend school. The courts have said that the obligation runs from the time of departure rather than arrival, that is, from when the offender leaves his former residence, job, or school rather than when he acquires a new residence or a new job or enrolls in a different school. SORNA defines broadly the terms "resides," "student," and "employee." For example "[t]he term 'resides' means, with respect to an individual, the location of the individual's home or other place where the individual habitually lives." The Attorney General's Guidelines observe that "[t]he scope of 'habitually lives' in this context is not self-explanatory and requires further definition." The Guidelines supply the state, territorial, and tribal authorities some guidance for the task. They point out that the term "habitually lives" may encompass instances where the offender "has no home or fixed address in the jurisdiction, or no home anywhere." Moreover, they state that "[t]he specific interpretation of this element of 'residence' which these Guidelines adopt is that a sex offender habitually lives in the relevant sense in any place in which … the sex offender lives in the jurisdiction for at least 30 days." This 30-day ceiling, however, "does not mean that the registration of a sex offender who enters the jurisdiction to reside may be delayed until after he has lived in the jurisdiction for 30 days. Rather, a sex offender who enters a jurisdiction in order to make his home or habitually live in the jurisdiction may be required to register within three business days." SORNA and the Guidelines provide comparable general definitions and minimum standards for the terms "employee" and "student." An "'employee' includes an individual who is self-employed or works for any other entity, whether compensated or not." The Guidelines here speak largely in terms of examples. For instance, they note that "a sex offender who resides in jurisdiction A and commutes to work in jurisdiction B must register and keep the registration current in both jurisdictions." Some of the examples are designed to alert the state, local, and tribal jurisdiction of challenges to be addressed. One representative illustration suggests that with respect to interstate truck drivers: If a sex offender has some employment-related presence in a jurisdiction, but does not have a fixed place of employment or regularly work within the jurisdiction, line drawing questions may arise, and jurisdictions may resolve these questions based on their own judgments. For example, if a sex offender who is long haul trucker regularly drives through dozens of jurisdictions in the course of his employment, it is not required [that] all such jurisdictions must make the sex offender register based on his transient employment-related presence, but rather may treat such cases in accordance with their own policies. A sex offender who is employed may not have a fixed place of employment - e.g ., a long-haul trucker whose 'workplace' is roads and highways throughout the country … Knowing as far as possible where such a sex offender is in the course of employment serves the same public safety purposes as the corresponding information regarding a sex offender who is employed at the fixed location. The authority under section 114(a)(7) [requiring registration employment information] is accordingly exercised to require that information be obtained and included in the registry concerning the places where such a sex offender works with whatever definiteness is possible under the circumstances, such as information about normal travel routes … in which the sex offender works. The definition of the term "student" is somewhat more confined. The term means "an individual who enrolls in or attends an educational institution, including (whether public or private) a secondary school, trade or professional school, and institution of higher education." The Guidelines explain that "enrollment or attendance in this context should be understood as referring to attendance at a school in a physical sense." In Nichols v. United States , the Supreme Court recently concluded that SORNA's requirements in place at the time did not apply when offenders relocated abroad. Anticipating the problem, Congress passed the International Megan's Law to Prevent Child Exploitation and Other Sexual Crimes Through Advanced Notification of Traveling Sex Offenders [Act], which among other things, amends SORNA to compel offenders to supplement their registration statements with information relating to their plans to travel abroad. Only those who have been convicted of a qualifying sex offense need register. There are five classes of qualifying offenses: (1) designated federal sex offenses; (2) specified military offenses; (3) crimes identified as one of the "special offenses against a minor"; (4) crimes in which some sexual act or sexual conduct is an element; and (5) attempts or conspiracies to commit any offense in one of these other classes of qualifying offenses. Certain foreign convictions, juvenile adjudications, and offenses involving consensual sexual conduct do not qualify as offenses that require offenders to register under SORNA. Federal qualifying offenses "(including an offense prosecuted under section 1152 or 1153 of title 18)" consist of those "under section 1591, or chapter 109A, 110 (other than section 2257, 2257A, or 2258), or 117, of title 18," that is: 18 U.S.C. §1591 (sex trafficking of children or by force or fraud) 18 U.S.C. §2241 (aggravated sexual abuse) 18 U.S.C. §2242 (sexual abuse) 18 U.S.C. §2243 (sexual abuse of ward or child) 18 U.S.C. §2244 (abusive sexual contact) 18 U.S.C. §2245 (sexual abuse resulting in death) 18 U.S.C. §2251 (sexual exploitation of children) 18 U.S.C. §2251A (selling or buying children) 18 U.S.C. §2252 (transporting, distributing or selling child sexually exploitive material) 18 U.S.C. §2252A (transporting or distributing child pornography) 18 U.S.C. §2252B (misleading Internet domain names) 18 U.S.C. §2252C (misleading Internet website source codes) 18 U.S.C. §2260 (making child sexually exploitative material overseas for export to the U.S.) 18 U.S.C. §2421 (transportation of illicit sexual purposes) 18 U.S.C. §2422 (coercing or enticing travel for illicit sexual purposes) 18 U.S.C. §2423 (travel involving illicit sexual activity with a child) 18 U.S.C. §2424 (filing false statement concerning an alien for illicit sexual purposes) 18 U.S.C.