One of Donald Trump’s first official actions as president was to sign an executive order designed to protect freedom of expression against government pressure. Soon after, Vice President J.D. Vance issued a vigorous challenge at the Munich Security Conference to speech restrictions in Europe. After years of government assaults on freedom of expression, people who cared about First Amendment values were cautiously optimistic. Then came the administration’s attempted deportation of Mahmoud Khalil. Khalil, a permanent legal resident of the United States who is married to an American citizen and...