In recent years, public officials and terrorism analysts have warned of a growing threat of Muslim homegrown terrorist attacks: attacks initiated by American Muslim citizens and residents against targets in the United States. Following the Madrid 2004 and London 2005 bombings, analysts became concerned that Muslims in the United States could be inspired to similar terrorist activity. A subsequent spike in 2009 in the number of American Muslims arrested on terrorism charges seemed to confirm that the phenomenon had taken root in the United States. Homegrown terrorism has since emerged as a major public policy concern. As Secretary of the Department of Homeland Security Janet Napolitano cautioned in February 2011, “One of the most striking elements of today’s threat picture is that plots to attack America increasingly involve American residents and citizens.” According to Attorney General Eric Holder, “The American People would be surprised at the depth of the [homegrown terrorist] threat.”
In reality, Americans do not have much to fear from Muslim homegrown terrorism and should be skeptical of claims that the threat is increasing. Close analysis reveals little evidence that Muslim Americans demonstrate either the will or capacity to plot attacks in the United States.
Assessing the depth of the terrorist threat requires, first, looking for evidence that growing numbers of Muslims in the United States are seeking to attack American targets. The logic here is straightforward: Unless more terrorists are motivated to initiate plots in the United States, there will be no more homegrown attacks. Unfortunately, evaluating precisely how many American Muslims are attracted to terrorism and will in the future engage in terrorist plotting is a difficult enterprise.
One potential starting point is the scholarly literature on the causes of “radicalization,” in which analysts evaluate the pathways through which individuals transform from regular people into aspiring terrorists. Such analyses catalogue the attitudinal and behavioral changes that precede an individual’s turn to terrorism and in some cases provide illuminating narratives about terrorists’ life histories. These studies, however, do not provide any evidence about the overall number or percentage of American Muslims who are motivated to engage in terrorism. They cannot even tell us whether individuals exhibiting the danger signs of radicalization will actually take the steps to plot an attack.
The limited evidence available that does speak to American Muslims’ support for terrorism suggests little basis for concern. An in-depth study of Muslim communities in the United States funded by the Department of Justice and led by the sociologist Charles Kurzman and his colleagues found that there is little support for militancy in these communities. This conclusion is echoed in public opinion surveys undertaken by the Pew Research Center.
If there is little evidence that American Muslims are increasingly drawn to terrorism, what, then, should we make of the fact that more have been arrested on terrorism offenses in recent years? Do those arrests not indicate growth in the incidence of homegrown terrorist activity?
Not necessarily. In fact, there are reasons why the number of people arrested on terrorism related charges may increase even if no more individuals are engaging in terrorist plotting. One reason is the growing array of tools available to law enforcement to detect terrorist activity, which increases the odds that activities that may in the past have been overlooked are instead discovered. Since late 2008, the FBI has been granted expanded authority to undertake “assessments” and open preliminary investigations of suspect Americans without first establishing a factual basis for the inquiry. According to the New York Times, for example, from March 31, 2009 to March 31, 2011, the FBI initiated more than 82,000 assessments of individuals and groups suspected of potentially being involved in terrorist activities in the United States.
Not only do officials have more leeway to investigate suspicious activity, they also have strong incentives to make sure they scour the environment for all evidence of terrorist activity. One motivation is to ensure that those accused of terrorism are actually charged with terrorist-related offenses or breaches of national security, rather than lesser charges, such as immigration violations. In addition, prosecutors often decline to pursue terrorism cases referred by law enforcement; this high declination rate generates incentives to uncover every bit of evidence necessary to ensure cases go forward. These efforts too contribute to the likelihood that potential terrorist activities will be detected that otherwise may have passed unnoticed. In short, greater investment in screening and latitude in investigations may be increasing the amount of terrorist activity uncovered by authorities.
Evidence of an increased probability of detection would be especially significant in light of law enforcement’s extensive use of sting operations against terrorism suspects. Sting operations are initiated when authorities identify an individual suspected of wanting to attack Americans but who has not yet developed a plan for doing so. Undercover agents or informants can provide the aspiring terrorist everything from rent money to fake explosive devices. They act as sounding boards and virtual co-conspirators as the individuals refine their plans. Although these suspected terrorists commonly exhibit the will to commit violence, it is this companionship and assistance that helps them to advance their plots and take concrete action on behalf of their ambitions. This is critical: Without assistance, these plots may have remained aspirational, never reaching the point of implementation and therefore never yielding arrests to be counted in terrorism statistics. By my account, of the 18 plots that reached some measure of operational readiness between September 2001 and December 2010, 12 involved informants or undercover agents at the formative phase of the plot, before perpetrators identified targets or sought out weapons. In short, the number of terrorist arrests provides a poor indicator of the underlying propensity of American Muslims to engage in terrorist plotting.
Even if more Muslims are attracted to terrorist activity, however, assessing the homegrown threat requires looking beyond just individuals’ motivations to initiate terrorist plots. It requires assessing their actual capabilities to execute deadly attacks. Here, too, the argument falls short that homegrown terrorism represents a growing threat to Americans.
There are at least two major problems facing Muslim homegrown terrorists in executing successful attacks. First, the United States presents a difficult security environment in which to be a modern-day terrorist; those who initiate plotting are apt to be detected and foiled by arrests before they can act on their plans. Second, homegrown terrorists lack the skills and savvy of seasoned international terrorists, rendering it difficult for them to navigate the country’s impermissive security environment and to carry out the technical tasks essential to executing an attack.
Take, to start, the nature of the security environment and the obstacles it presents. Although a variety of factors render the United States inhospitable to terrorist plotting, crucial is the lack of support for militancy by members of the Muslim community, which deprives aspiring terrorists of sanctuary as they prepare attacks. Muslim communities engage in substantial self-policing, seeking to deter the turn to militancy by members of their communities, and if that fails, they commonly report suspected militants to authorities. A study by Syracuse University, for example, found that from 2001 through 2010, in 22 percent of all cases in which a defendant was charged with some terrorist related offense, unsolicited tips from family or community members brought the person to law enforcement’s attention.
The empirical record of successful attacks in the United States also underscores the difficultly of engaging in terrorist plotting without being detected. Since 9/11, there have been only two successful attacks in the United States: Major Nidal Hasan’s Fort Hood attack and a lesser known shooting by the Muslim convert Carlos Bledsoe outside an Arkansas recruiting station, which harmed two soldiers. All those who have sought to prepare a terrorist attack in the United States, with the apparent exception of Times Square bomber Faisal Shahzad, have been known to law enforcement before they executed the plot, including Hasan and Bledsoe.
In addition to constraints posed by the security environment, the amateur nature of the pool of aspiring terrorists in the United States complicates efforts to execute deadly attacks. These individuals are not part of a hardened cadre of foreign fighters or the well-vetted and trained operatives that al Qaeda used for the 9/11 attacks. Rather, they lack experience in carrying out essential tasks, such as those necessary to safeguard their plots from exposure. A recent survey of cases revealed that aspiring homegrown terrorists commonly make rudimentary mistakes in operational security, such as advertising their intentions online or otherwise attracting the attention of regular citizens who then report them to authorities.
These amateurs also lack technical skills, such as the ability to fabricate bombs, which remain the weapon of choice for terrorists. In this regard, some might point to the Internet or overseas training as helping terrorists overcome their inadequacies, thereby intensifying the homegrown threat. By providing easily accessible expertise and instructional guidance, for example, the Internet could compensate for a lack of formal training. Studies of bomb-making manuals, however, reveal online information to often be spotty and poorly organized. Moreover, an aspiring bomb-maker needs the opportunity to practice and experiment under local conditions.
Overseas training also poses unique challenges for those seeking to build their terrorist skill-set. Not least is proving to leaders of the overseas militant organization that one is not an operative of a foreign intelligence agency and is, in fact, a good candidate for training. Some who have sought out training have been rejected because of their unproven credentials. Even if aspiring terrorists do manage to acquire overseas training, however, it remains of uncertain benefit once they return to the United States. The plot, for example, that officials cite as the most serious since 9/11—Najibullah Zazi and his co-conspirators’ alleged plan to bomb the NYC subway—ran into trouble when, despite having received overseas instruction, Zazi stumbled when formulating his peroxide bomb. He reportedly emailed his overseas contacts for help, and those communications were intercepted. Shahzad, the Times Square bomber, also received overseas training, but he too had trouble crafting a viable bomb. Part of the problem, according to the New York City police commissioner, was that Shahzad deliberately selected an inferior grade ammonium nitrate fertilizer for his device, in order to lessen the chances his purchases would be detected. His case demonstrates how the security environment in the United States can elevate the skills necessary to be an effective terrorist, by forcing individuals to rely on more complex bomb-making technologies.
Indeed, an implicit recognition of these obstacles may be why analysts increasingly emphasize the threat of “lone-wolf” homegrown terrorist attacks. That there have been few such attacks, despite their operational simplicity, however, suggests either that there are no aspiring terrorists in the country or that plotters of even simple terrorist attacks are being detected or deterred before they can harm Americans.
In sum, under close scrutiny the homegrown terrorist threat looks far less threatening than public officials often claim. There are, moreover, serious consequences to exaggerating the threat posed by Muslim Americans.
To start, overstating this threat could lead to the misallocation of increasingly scarce federal, state, and local law enforcement resources. As the United States enters an era of fiscal austerity, officials must evaluate the opportunity costs of investing in domestic counterterrorism versus other priorities. Consider, for example, how the FBI’s shift in resources from white collar crime to counterterrorism after the September 11 attacks reduced the agency’s capacity to handle cases of mortgage and securities fraud at the height of the financial crisis. While a balance must be struck in financing domestic counterterrorism, recent sting operations required dozens of agents and officials per investigation. Serious questions need to be asked by government officials and by the American public regarding what qualifies as the appropriate nature and amount of investment in domestic counterterrorism.
In addition, overstating the threat of Muslim homegrown terrorism could lead to the adoption of counterproductive counterterrorism methods. Methods commonly employed by law enforcement in Muslim communities, such as extensive surveillance and cultivation of informants, are inherently challenging for any segment of society to endure, even when agents treat them with care. And a careful approach is rarely encouraged by an atmosphere of suspicion. Recent controversies associated with the New York City Police Department and its Counterterrorism Bureau underscore these risks. These controversies include the 2011 arrest of Jose Pimental, in whose case the FBI declined to become involved when questions arose about the role of the NYPD’s informant in the sting operation; reports by the Associated Press that the NYPD spied on members of the Muslim community, such as Imam Sheikh Rada Shata, who had previously cooperated with authorities in their counterterrorism initiatives; or evidence that the NYPD used a film with inflammatory claims about Islam in its training programs.
Controversies of this kind undermine the relationships of trust that form the basis for cooperation between Muslim communities and public officials. Yet these communities have demonstrated a willingness and a capacity to report signs of terrorist activity in their midst, and their help is both the most efficient and least invasive method of exposing aspiring militants. Alienating those who would provide such information will carry a heavy cost.
Finally, exaggerating the threat posed by homegrown Muslim terrorists leads to a distorted image of the nature of domestic terrorism in the United States that is harmful to the social fabric of the country. While small in number, acts of domestic terrorism in the United States involve individuals of diverse ideological extremes. Domestic terrorism may encompass violent splinters from the Occupy Movement, anti-government militants like the “Sovereign Citizens,” or Islamist jihadis—among others. Exaggerating threats from Islamist militancy at the expense of a more comprehensive discussion of domestic terrorism not only contributes to mistrust between Muslim Americans and other Americans, it is counter to the country’s long heritage of respecting people of diverse religions and backgrounds.
 Janet A. Napolitano, “Understanding the Homeland Threat Landscape—Considerations for the 112th Congress,” testimony before the United States House of Representatives Committee on Homeland Security, 112th Cong., 1st sess., February 9, 2011.
 “Home-grown, solo terrorists as bad as Al Qaeda; FBI chief,” Agence France Presse, April 15, 2010. Pierre Thomas, Jason Ryan and Theresa Cook, “Holder Homegrown Terror Threat Increasing” Abcnews.com July 2009. David Schanzer, Charles Kurzman, and Ebrahim Moosa, “Anti-Terror Lessons of Muslim-Americans,” Doc. No. 229868 (Washington, D.C.: National Criminal Justice Reference Service, 2010), page 10.
 For details on studies see Mark Sedgwick, “The Concept of Radicalization as a Source of Confusion,” Terrorism and Political Violence 22, no. 4 (October 2010): 479–494.
 Schanzer, David, Charles Kurzman, and Ebrahim Moosa. “Anti-Terror Lessons of Muslim-Americans,” (pdf) doc. no. 229868. Washington, D.C.: National Criminal Justice Reference Service, 2010.
 Pew Research Center, “Muslim Americans: Middle Class and Mostly Mainstream” (Washington, D.C.: Pew Research Center, May 22, 2007); Pew Research Center. “Muslim Americans: No Signs of Growth in Alienation or Support for Extremism.” (pdf) Washington, D.C.: August 30, 2011.
 Charlie Savage of the New York Times has reported extensively on the 2008 guidelines and the expanding authority of federal agents to undertake “assessments” of Americans without establishing first a factual basis for the inquiry. Significantly, the guidelines have rendered it easier to employ human sources, or informants. See, from the New York Times, “F.B.I. Cases Wide Net Under Relaxed Rules for Terrorism Inquiries,” March 26, 2011; “F.B.I. Agents Get Leeway to Push Privacy Bounds,” June 12, 2011; “F.B.I. Focusing on Security Over Ordinary Crime,” August 23, 2011. Documents provided to Savage under the Freedom of Information Act appear here.
 Discussed in “Terrorist Trial Report Card: September 11, 2001–September 11, 2010” (New York: Center on Law and Security, New York University Law School, 2010). For illustrations of these dynamics see “Terror Plot Foiled: Inside the Smadi Case,” Federal Bureau of Investigation, November 5, 2010,; Mike Robinson, “FBI Stays Undercover Longer to Aid Prosecution of Alleged Plotters,” Virginian-Pilot, September 26, 2009.
 “Who Is a Terrorist? Government Failure to Define Terrorism Undermines Enforcement, Puts
Civil Liberties at Risk” (Syracuse, N.Y.: Transactional Records Access Clearinghouse [TRAC], September
2009). The declination rate includes all terrorism cases referred for prosecution in the United States.
 Risa Brooks, “Muslim ‘Homegrown’ Terrorism in the United States: How Serious is the Threat,” International Security 36, no. 2 (fall 2011).
 Schanzer, Kurzman, and Moosa, “Anti-Terror Lessons of Muslim-Americans.”
 “Post-9/11 Jihadist Terrorism Cases Involving U.S. Citizens and Residents: An Overview” (Washington, D.C., and Syracuse, N.Y.: New America Foundation and Maxwell School, Syracuse University, n.d.). The study includes all “post-9/11 jihadist cases” involving terrorist-related offenses, not just attacks in the United States. It also found that 35 percent of terrorist cases have involved an informant. Another 9 percent of cases involved undercover officers exposing plots. Also see Kevin Strom, John Hollywood, Mark Pope, Garth Weintraub, Crystal Daye, and Don Gemeinhardt, “Building on Clues: Examining Successes and Failures in Detecting Terrorist Plots, 1999–2009” (Research Triangle Park, N.C.: Institute for Homeland Security Solutions, October 2010).
 Mueller, John, ed. Terrorism since 9/11: The American Cases (pdf). Columbus: Mershon Center, Ohio State University, 2011.
 Anne Stenerson, “The Internet: A Virtual Training Camp?” Terrorism and Political Violence Vol 20, No. 2 (April 2008), pp. 215–233., Jennifer Yang Hui, “The Internet in Indonesia: Development and Impact of Radical Websites,” Studies in Conflict and Terrorism, Vol. 33, No. 2 (February 2010), pp. 171–191,
 Kenney, Michael. “Beyond the Internet: Mētis, Techne, and the Limits of Online Artifacts for Islamist Terrorists,” Terrorism and Political Violence Vol. 22, no. 2 (April 2010): 177–197.
 Take the case of five Muslim American suspects who traveled to Pakistan for training but were repeatedly turned down “because they were foreigners and had no local references.” See Jim Sciutto and Pierre Thomas, “Terror Wannabes? Arrested Americans Rejected for Jihad Training,” ABC News, December 10, 2009.
 Anahad O’Connor, “Weak Times Sq. Car Bomb Is Called Intentional,” New York Times, July 21,
2010; and Peter Grier, “Why the Times Square Bomb Failed Spectacularly,” Christian Science Monitor, May 3, 2010.
 Eric Lichblau, David Johnston, and Ron Nixon, “F.B.I. Struggles to Handle Financial Fraud Cases,” New York Times, October 18, 2008. See also Paul Shukovsky, Tracy Johnson, and Daniel Lathrop, “Focus on National Security after 9/11 Means That the FBI Has Turned Its Back on Thousands of White-Collar Crimes: The Terrorism Trade-Off,” Seattle Post-Intelligencer, April 11, 2007.
 On these incidents see William K. Rashbaum and Joseph Goldstein, “Informer’s Role in Terror Case Is Said to Have Deterred F.B.I.,” New York Times, November 21, 2011; “AP Series on Surveillance Wins Pulitzer,” David Crary, Associate Press, April 16, 2012, showing of the film was originally reported by Tom Robbins, “NYPD Cops’ Training Included an Anti-Muslim Horror Flick,” Village Voice, January 19, 2011.
 Risa Brooks, “Homegrown Terror isn’t just Islamist,” CNN.com, May 3, 2011.