After 13 U.S. troops were killed during the opening weeks of the Iran war, Joe Kent had seen enough. It was time, he said, to stand on principle and resign his position as director of the National Counterterrorism Center, knowing it was likely that some of President Donald Trump’s other advisers would turn on him. Kent, a retired Special Operations soldier whose military career included 11 combat deployments, had decided days earlier that if hostilities with Iran erupted into a “full war like we’re doing now,” then there was no way he could stay. Doing so, he reasoned, would have...