Material Support of Terrorism Looms over Supreme Court’s Social Media Case

On February 22, 2023, the Supreme Court heard oral argument in Twitter v. Taamneh. The case concerns an act of violence committed by ISIS in a Turkish nightclub in 2017. In bringing suit in the lower courts, plaintiffs alleged that Twitter, Facebook, and Google aided and abetted ISIS’s attack, in violation of 18 U.S.C. § 2333(d), by allowing their platforms to be used by the group to recruit adherents and spread propaganda, amongst other things. Under Section 2333(d), U.S. citizens can bring tort suits against those who aided and abetted a designated foreign terrorist organization (FTO), such as ISIS, that committed acts of international terrorism that injured them. In passing Section 2333(d), Congress directed courts to construe the statute in accordance with the D.C. Circuit case of Halberstam v. Welch, which sets out a multi-part test for establishing civil aiding-and-abetting liability.

In Taamneh, the parties’ dispute centers around the scope of aiding-and-abetting liability under Section 2333(d) and Halberstam. This case is not, however, just about the relevant framework for aiding and abetting under federal civil law. It is also about the broadly defined concept of “material support” to terrorism and prevailing understandings of the so-called “nature” of terrorist organizations themselves. These issues were last addressed by the Court in the 2010 case Holder v. Humanitarian Law Project. Holder dealt with the scope of the criminal statute prohibiting material support to certain terrorist groups, 18 U.S.C. § 2339B. Various parts of that decision loom in the background of Taamneh.

The Dispute in Taamneh

While the parties have briefed a variety of issues, Holder’s relevance to Taamneh is most clearly reflected in the parties’ dispute over what defendant’s aid must be directed towards, as well as the kinds of support that constitute aiding and abetting under Section 2333(d). In order to address these questions, the Court has little choice but to grapple—at least implicitly—with Holder and its approach to material support and the terrorist groups that receive it.

Under Section 2333(d), defendant needs to “aid[] and abet[], by knowingly providing substantial assistance . . . [to] the person who committed such an act of international terrorism.” Petitioners Twitter et al—and the U.S. government, which has submitted an amicus brief in this case—argue that defendant’s aid must go to an FTO’s violent activities. Respondents say the aid just needs to go to the FTO itself.

Halberstam’s multi-pronged, aiding-and-abetting test additionally requires that defendants aid must go to the “principal violation” committed by the FTO. Petitioners—and perhaps the government too, at least at oral argument—argue that the “principal violation” is the specific act of terrorism that injured plaintiff. By contrast, respondents insist that the principle violation is the “terrorist enterprise” itself.

Finally, the parties argue over the kind of support that can constitute knowing and substantial assistance under Halberstam. Petitioners—and the government—question whether routine and widely available business services can qualify, without some heightened showing of liability. Respondents insist that those kinds of services can and should qualify and reject any requirement of heightened liability.

In sum, on respondents’ view of Section 2333(d), Twitter and the other defendants just need to have aided and abetted ISIS while the group was otherwise engaged in a general campaign of terrorist violence. Another way of putting this is that aid to ISIS amounts to aid to its terrorist activities writ large—the two are one and the same. For respondents, the kind of aid provided does not matter, as long as the other elements of aiding-and-abetting liability are met. By contrast, on Twitter et al’s view, defendants must have aided ISIS in the specific act of violence that injured plaintiffs. On this approach, not just any kind of aid will qualify as aiding and abetting—routine, widely available business services usually will not—especially if the aid is not traceable to the act of violence itself.

Broader Issues Raised in Holder

While these disputes could possibly be resolved simply by parsing the text of Section 2333(d) or Halberstam, the reason they have arisen at all is because of particular views about terrorism and terrorist groups that are reflected in Holder. These notions include an expansive view of material support, the purported fungibility of such support, and the so-called taint that hangs over all terrorist organizations. These concepts are not unique to Holder—indeed, they are long-standing U.S. government policies, reflected in federal law, and otherwise embraced by both Congress and the executive branch. That these policies are reflected in Holder is, however, particularly relevant here since Holder represents both the first and last time the Court was squarely confronted with those policies.

On the first policy—the broad definition of material support—Holder doubled down on an expansive and largely unrestricted view of what constitutes material support to terrorist groups. As defined by statute, material support includes “any property, tangible or intangible, or service, including currency or monetary instruments or financial securities, financial services, lodging, training, expert advice or assistance, safehouses, false documentation or identification, communications equipment, facilities, weapons, lethal substances, explosives, personnel. . . and transportation, except medicine or religious materials.” Under this definition, almost any kind of aid to a terrorist group—no matter how innocuous or mundane—qualifies as material support. In Holder, the Court rejected plaintiffs’ argument that elements of this definition were quite vague—terms, like “service,” are not even defined by the statute—and refused to meaningfully cabin material support’s expansive reach in any way.

On the second policy—fungibility—Holder threw its weight behind the notion that all material support to a terrorist organization—including support that promotes peaceful, lawful conduct—is fungible and interchangeable. Support for a terrorist group’s peaceful activities can, for example, “lend legitimacy to foreign terrorist groups . . . all of which facilitate more terrorist attacks” in the Court’s view.  Because support is fungible, it is necessarily untraceable, making it impossible to know whether one’s support has actually gone to the group’s peaceful activities or to its violent ones.

Third and relatedly, on taint, Holder adopted the view that any material support provided to a terrorist organization necessarily supports its terrorist violence. As the Court noted, “‘foreign organizations that engage in terrorist activity are so tainted by their criminal conduct that any contribution to such an organization facilitates that conduct.’” (emphasis added).

Holder’s Broader Issues in Taamneh

All of these concepts are reflected in respondents’ and petitioners’ arguments in Taamneh about what defendant’s aid must be directed towards, as well as the kinds of support that constitute aiding and abetting under Section 2333(d). While respondents’ position on these issues is a mirror image of Holder, petitioners’ view is its antithesis.

Starting with respondents, though the Taamneh case does not directly address the material support concept, respondents’ insistence that providing social media services can aid and abet terrorism certainly aligns with the expansive view of material support reflected in federal law and ratified in Holder. Respondents also embrace the notion that any kind of support to a terrorist group—even support that does not directly contribute to violence—aids and abets that group’s terrorism. This position aligns with the Holder view that terrorist groups are so “tainted” by their terrorist activity that support for such groups will necessarily contribute to their terrorist acts. Finally, in their brief, respondents vociferously reject the notion that defendant’s support must be traced to the specific terrorist activity that causes plaintiff’s injury. In their view, support to terrorist groups is “fungible” and cannot be traced to particular terrorist attacks. Indeed, respondents include various citations to Holder on this point.

As for petitioners, their positions challenge the view of material support and nature of terrorist organizations reflected in Holder. For example, Twitter et al argue that the provision of routine, widely available services to a terrorist group should not, without more, be viewed as aiding and abetting terrorist violence—a position that is in tension with the broad definition of material support embraced by Holder. In demanding a direct connection between defendant’s aid and the commission of a specific terrorist attack, petitioners also reject the Holder view that any support to a terrorist group necessarily supports its terrorist violence. For petitioners, aid must be traced to a particular act of terrorism, otherwise the scope of the aiding-and-abetting statute will have an “impossible breadth”—again, a notion that challenges the Holder view about the fungibility of material support.

What Will the Supreme Court Do?

In deciding this case, it seems, then, that the Court will necessarily have to weigh in on the government policies regarding material support and terrorist groups that Holder embraced, at least implicitly. This is not, however, the first time those policies have loomed over a Section 2333 suit. As I have previously written, those concepts have long been at the heart of judicial approaches to Section 2333(d)’s sister statute, 18 U.S.C. § 2333(a). Section 2333(a) establishes primary civil liability for material support and other forms of involvement in international terrorism and predates Section 2333(d)—which was passed in 2016—by over 20 years. Embracing Holder-like views on material support and terrorist groups, courts have largely used those policies to eviscerate both the scienter and causation elements of Section 2333(a).

At oral argument, some justices seemed concerned about a reading of Section 2333(d) that could conceivably reach any and all kinds of support to FTOs. Indeed, Justice Kavanaugh—surprisingly—expressed concern about how an expansive approach to Section 2333(d) would impact charities and humanitarian organizations. Respondents themselves also present a parade of horribles in their briefs about how countless businesses and non-profits will be negatively impacted by a reading of Section 2333(d) that aligns with respondents’ positions. Even the U.S. government expressed concern at oral argument about the consequences of an expansive interpretation of the statute.

These are not new concerns. Section 2333 cases—under both Section 2333(a) and 2333(d)—have long targeted third-party defendants, such as banks, charitable organizations, advocacy groups, social media companies, and even individuals for providing material support to terrorism on loose theories of liability. Taamneh is just the tip of the iceberg.


In Holder, the Court shrugged off concerns about the negative effects of material support’s broad definition, as well as the consequences of conflating support to terrorists with support for terrorist violence itself. That case involved NGOs providing innocuous forms of material support to terrorist groups—this time a group of large and influential American corporations are caught in the crosshairs of U.S. counter-terrorism policy. In Taamneh, the U.S. government has seemingly pulled back from its typically expansive approach to prohibiting any and all forms of material support to terrorist groups. One hopes the Supreme Court will follow suit.