As a researcher who has spent more than two decades studying counterterrorism and radical Islamist organizations in the Middle East, I want to address the Department of Homeland Security directly — and its new secretary, who understands the nature of the regime ruling Iran. The threat posed by the Islamic Republic on American soil is not hypothetical. Its record reveals an operational pattern of proxy terrorism, criminal recruitment, target surveillance, and assassination plots.

In March, the Justice Department announced the conviction of a trained operative connected to the Islamic Revolutionary Guard Corps in a plot to assassinate American political figures; evidence presented in the case identified President Donald Trump among the potential targets. The FBI has likewise warned of Iranian plots against former U.S. officials. The danger is more acute after seven months of war have left Tehran weakened, humiliated, and increasingly isolated, while Russia and China have proved less dependable than its rulers imagined. A regime sustained largely by two machines — propaganda and repression — now confronts an Iran approaching potentially historic upheaval.