While working on terrorism-related issues during my congressional career, I soon understood not only that Iran had earned its reputation as the world’s leading state sponsor of terrorism, but also that the country’s leadership considered terrorism a viable replacement for standard political and diplomatic statecraft. A recent criminal court ruling in Belgium reinforces this fact. Since the time of the 1979 revolution, the use of proxies in terror operations abroad afforded the regime some measure of plausible deniability and made it more difficult for the U.S. or its allies to hold Iranian officials directly accountable. Still, it was shocking when...