How Do You Prosecute an American Radical?

On April 14th, 2026, The Program on Extremism's "The Threat" Substack hosted a live conversation titled "How Do You Prosecute an American Radical?". It featured Dr. Omar Mohammed and Barry Jonas, Senior Research Fellows at the Program on Extremism. Jonas, spent over 34 years at the Department of Justice. The conversation examined the legal mechanics of prosecuting Americans who embrace extremist ideology and align with foreign terrorist groups.

Jonas began by laying out the core statute prosecutors rely on, which criminalizes providing "material support" to a Foreign Terrorist Organization, or FTO. An FTO designation is issued by the U.S. State Department, after interagency consultation, for organizations such as Hezbollah that commit terrorism against U.S. interests. Once an organization is designated, it becomes illegal for any "U.S. person" - a term covering citizens, green-card holders, and anyone present in the U.S. regardless of legal status - to provide it material support, whether the support is given domestically or from overseas, since U.S. jurisdiction follows the person abroad. Material support is defined broadly to include almost anything except medical supplies and religious materials, encompassing money, weapons, and equipment, but also people, since traveling to join a group counts as material support in itself, and services. For services specifically, including the media and propaganda work that Jonas said dominated his caseload in his final years as a prosecutor, the law requires that the person act at the direction and control of, or in coordination with, the terrorist group; a group's general call to its followers still counts if a follower acts on it.

Jonas repeatedly stressed a bright line: the United States does not prosecute ideology or belief, only acts done in coordination with a designated group. Waving an ISIS flag and declaring support for it in front of the White House is protected First Amendment speech, he explained, unless done because ISIS instructed its followers to do so, at which point it becomes material support. Simply holding or voicing extremist views, including views sympathetic to Iran or Hezbollah, is not illegal by itself. Applied to Calla Walsh, a U.S. citizen believed to be in Lebanon publicly expressing support for the IRGC and Hezbollah, both FTOs, Jonas said whether she can be prosecuted turns on whether the FBI and DOJ can show she is acting independently, which would be protected speech, versus in coordination with those groups, which would be a crime. He said he assumed the FBI was likely investigating but had no inside knowledge, having left the government roughly eight or nine months earlier.

Turning to evidentiary challenges, Jonas identified evidence-gathering, not legal authority, as the main obstacle to prosecuting Americans radicalized or operating overseas. The U.S. retains jurisdiction over its citizens and persons regardless of where the conduct occurs, unlike an ordinary foreign crime such as a bank robbery in Germany, which the U.S. has no interest in prosecuting, but classified intelligence about a person's overseas conduct often cannot be used in court as admissible evidence. Practical evidence sources, he said, include phone data collected or "dumped" at the U.S. border upon a person's return, showing messages, photos with group members, or weapons; online communications, including chats where an FBI undercover agent may be present; and statements made publicly or online which, while not independently criminal, can help establish intent. Encrypted apps like Signal complicate remote surveillance, he noted, since agents generally need physical access to a device to read encrypted messages, as a warrant alone will not unlock encrypted content on Signal's servers.

Jonas explained that the material support statute allows prosecution not only for successfully aiding a group but also for conspiracy or attempt, enabling preventive arrests. He cited the earlier wave of "traveler cases," in which people were arrested at U.S. airports attempting to fly to join ISIS before ever boarding a plane, let alone reaching Syria or Iraq. Applied hypothetically to Walsh, he said, if she is in Hezbollah-controlled territory in Lebanon and has expressed an intent to join the group, she could be prosecuted for attempting material support even if Hezbollah never formally accepts her. Asked by Mohammed whether recruiting others counts as material support even absent a physical or monetary transaction, Jonas confirmed that recruitment is a "service" that can qualify, though intent and coordination remain decisive: starting a Hezbollah-affiliated cell because the organization directed followers to do so is a crime, while starting a group independently, on one's own initiative, is a closer legal question that is not automatically criminal, though prosecutors would examine the purpose behind it, and evidence of true intent typically leads to prosecution. He noted a related but separate offense as well: if a person who traveled abroad and potentially joined a terrorist group later lies to the FBI when asked about it, that lie is itself a prosecutable crime, though proving it typically requires much of the same evidence needed to prove the original material-support offense.

Mohammed pressed Jonas on how the law treats hate speech, such as antisemitism, directed at groups rather than material support provided to organizations. Jonas distinguished several categories: hate speech itself, however offensive, is protected by the First Amendment and not independently prosecutable, with flag-burning serving as the classic Supreme Court example of protected, if reviled, expression. Hate crimes, by contrast, are ordinary crimes such as assault that are enhanced or specially charged because they were motivated by a victim's protected characteristics, with the underlying hateful speech usable as evidence of motive or intent even though the person is prosecuted for the act rather than the belief. Incitement represents another point where speech crosses into criminal conduct, such as directly urging and equipping someone to commit a specific violent act; Jonas acknowledged a grey area between merely provocative rhetoric and actionable incitement but said that where speech leads to or facilitates an act, the line has been crossed. He pointed listeners to a related Program on Extremism panel he participated in during March, focused specifically on where speech crosses the line into criminality, available on the Program's website and YouTube channel.

Jonas also confirmed there is no formal U.S. legal definition of "extremism." There is a legal definition of terrorism, both domestic and international, covering an act of violence intended to intimidate or coerce a civilian population or government, but absent an act of violence tied to that intent, "extremism" remains a political and analytical term rather than a prosecutable legal category.