Luis Alberto Castillo, a father of one from Venezuela, entered the United States on Jan. 19, one day before Donald Trump became president for a second term — swept into office on a promise to treat undocumented migrants with a heavy hand.
By Feb. 4, Mr. Castillo was on a plane to a U.S. Navy base at Guantánamo Bay in Cuba, best known for a detention center that has long held terrorism suspects accused of launching the deadliest attack on American soil.