President Trump instructed the Pentagon to resume nuclear testing after a 33-year pause, citing other nations’ capabilities. “That process will begin immediately,” the president wrote on social media. The directive took even many of Trump’s advisers off guard, according to officials, leading to unanswered questions about when, or if, the testing would actually begin. Historically, it is the Department of Energy that maintains and tests the US nuclear stockpile, not the Department of Defense.