S ince 2014, the Islamic State (IS) has become the focal point for the bulk of homegrown violent jihadist terrorist plots. This includes instances in which people in the United States wanted to travel to Syria to fight with extremist groups in the nation's civil war as well as plots to strike domestic targets. Regarding the former, in early 2016, U.S. government officials estimated that about 250 Americans had traveled (or tried to travel) to Syria to fight in the civil war—about 25 had been killed. Regarding the latter, in recent congressional testimony, the Director of National Intelligence, James R. Clapper noted that homegrown actors "will probably continue to pose the most significant Sunni terrorist threat to the U.S. homeland in 2016." Most homegrown IS acolytes have attempted to travel to Syria to join the terrorist group. The ideological goals undergirding the Islamic State's efforts to violently impose a caliphate in Iraq and Syria have attracted many of them. Some have sought adventure. Others have appeared to crave escape, camaraderie, even marriage. The Islamic State entices supporters via the Internet and social media. According to CRS analysis of publicly available information, IS supporters have accounted for 67 homegrown violent jihadist plots between 2014 and early June 2016. In the same time period, IS-linked plots have dominated the homegrown violent jihadist landscape, accounting for 67 of 76 total plots. In November 2015, the Federal Bureau of Investigation (FBI) reportedly had more than 900 investigations of IS suspects in the United States. Coping with the comparative size of this threat is one of the challenges domestic law enforcement agencies face. This is complicated by the varied courses of action chosen by IS supporters as they engage with the terrorist group. The 67 homegrown IS-plots can be broken into three rough categories based on the courses of action that plotters pursued as they attempted to support the terrorist group. (See Figure 1 .) The first two categories focus on foreign fighters, the last on people willing to do harm in the United States: The Departed — American foreign fighters who plan to leave or have left the United States to fight for the Islamic State. This group includes suspects scheming to travel but who are caught before they arrive in IS territory. The Returned — American foreign fighters who trained with or fought in the ranks of the Islamic State and return to the United States, where they can potentially plan and execute attacks at home. The Inspired — Americans lured—in part—by IS propaganda to participate in terrorist plots within the United States. The desire to become a foreign fighter (captured in either the departed or the returned category) played a role in 41 of the 67 IS-related plots. Almost all of the 41 had people either departing the United States for Syria or considering such a trip. Two of the 41 cases involved investigations of people who had returned from the conflict zone. Together, the 41 plots accounted for more than two-thirds of homegrown IS acolytes. In other words, it seems more often than not, the allure of the Islamic State has encouraged would-be violent jihadists to journey to Syria rather than strike a domestic target. However, this is not to suggest that the Islamic State discourages Americans from staying put and committing acts of terrorism. To the contrary, the Islamic State has incited would-be followers to stay in their home countries to commit terrorist acts. For example, in May 2016, the group issued an audio recording, particularly encouraging American and European sympathizers to commit attacks in their home countries during the holy month of Ramadan (early June to early July). The January 2016 issue of Dābiq , the Islamic State's English language magazine, praises the married couple reportedly involved in the San Bernardino shooting in December 2015. In 28 cases since the start of 2014, people inspired by the terrorist group's propaganda considered striking targets in the United States. Five of these succeeded. According to CRS estimates, 5 of the 13 homegrown violent jihadist attacks that have occurred since 9/11 involved people inspired by the Islamic State. It does not appear that any of the suspects in either the five IS-inspired attacks or the eight others had sustained, substantive, in-person contact with foreign terrorist organizations. In essence, these attacks involved do-it-yourself—DIY—terrorists. Largely isolated from the operational support of terrorist organizations, they acquired violent skills (however rudimentary) by themselves or relied on abilities that they had developed prior to becoming violent jihadists. Such DIY-ers often scraped together ideological justification for their deeds from online or social media sources aligned with terrorist organizations. Some drew inspiration from charismatic figures like now-dead radical U.S.-born imam Anwar al-Awlaki, who was affiliated with the terrorist group Al Qaeda in the Arabian Peninsula. Awlaki died in a widely reported U.S. strike in Yemen in 2011. As mentioned above, five attacks involved people who reportedly supported the Islamic State. On June 12, 2016, Omar Mateen reportedly shot and killed at least 49 people in a gay nightclub in Orlando, FL. He allegedly wounded more than 50 others. Mateen was killed by police. He claimed allegiance with the Islamic State during a 911 phone call he purportedly made during the attack. His immediate motives remain unclear. On January 7, 2016, Edward Archer allegedly shot an on-duty Philadelphia, PA police officer three times in the arm. The wounded man survived. Archer reportedly assaulted the officer while the latter was in his patrol vehicle. The FBI is investigating the incident as an act of terrorism. After the attack, the reputed assailant confessed to the crime and mentioned the Islamic State. On December 2, 2015, husband and wife Syed Rizwan Farook and Tashfeen Malik reportedly killed 14 people and injured 22 others in a shooting incident at the Inland Regional Center, a social services facility in San Bernardino, CA. The couple appeared to have targeted employees attending a holiday lunch and training session for San Bernardino County's health department, where Farook worked. Both died in a shootout with police after the attack on the Inland Regional Center. The FBI has noted that the day of the shooting, "a post on a Facebook page associated with Malik" pledged allegiance to Abu Bakr al Baghdadi, the leader of the Islamic State. In 2011, Farook allegedly began to plot a terrorist attack with a neighbor, Enrique Marquez, Jr., a U.S. citizen. They purportedly targeted a stretch of State Route 91 and the Riverside Community College in California, and "planned to use firearms and explosives to carry out the terrorist attacks." Two rifles Farook and Marquez obtained for their planned attack were used in the San Bernardino shooting. The neighbors did not carry out their highway and college plot, in part, because arrests in an unrelated FBI counterterrorism investigation in Southern California made them wary. Their scheme was never detected by law enforcement. Additionally, it appears that Farook helped to radicalize Marquez by introducing him to extremist ideology and the work of Anwar al-Awlaki. In November 2015, Faisal Mohammad, an 18-year-old, stabbed a fellow student and attacked three others at the University of California, Merced campus. In March 2016, the FBI announced that its investigation of the incident uncovered evidence that Mohammad may have been inspired by Islamic State propaganda. In May 2015, Elton Simpson and Nadir Soofi were shot and killed by local law enforcement in Garland, TX, as they tried to attack an exhibition of cartoons depicting the prophet Muhammad. A security guard was wounded in the altercation. Simpson purportedly had a pro-Islamic State social media account and claimed Awlaki as an inspiration. A third individual, U.S. citizen Abdul Malik Abdul Kareem, conspired with Simpson and Soofi but was not directly involved in the shootout in Garland. In March 2016, Kareem was found guilty of attempting to provide material support to the Islamic State as well as other charges. Aside from the three categories based on the courses of action that IS supporters follow, at least two other sorts of IS foreign fighters pose some threat to U.S. interests. The Lost: unidentified Americans who fight in the ranks of the Islamic State. Such individuals may come home after fighting abroad and remain unknown to U.S. law enforcement. Some American IS fighters will never book a trip back to the United States. (The post 9/11 record of U.S. counterterrorism investigations suggests this prospect. None of the Americans who have fought for al-Shabaab, a terrorist group based in Somalia, are known to have come home to plot attacks.) Finally, some American IS supporters will perish abroad. The Others: foreign IS adherents who radicalize in and originate from places outside of the United States or non-American foreign fighters active in the ranks of the Islamic State. These persons could try to enter the United States from abroad. In the broadest of senses, confronting the threats posed by IS acolytes categorized as the departed, returned, inspired, lost, and others requires U.S. law enforcement to identify individuals who present a danger as terrorists and preempt their efforts to do harm. All of this draws on resources, strategies, and programs developed largely in response to 9/11. Beyond these established programs, additional law enforcement efforts specifically targeting the Islamic State have been made. The following discussion is not intended as an exhaustive analysis of federal law enforcement counterterrorism efforts in the homeland. It is meant to broadly inform policy makers on such activity. For the United States, systematically identifying potential terrorists involves the country's watchlisting regimen. The datasets in the regimen include identities linked to the Islamic State.