In a sweltering Rose Garden on Thursday, as President Donald Trump intoned at length about restoring faith to the White House, he took a moment to single out a man sitting right up front. “When I have a problem, I call up Marco,” Trump told his crowd, gesturing toward Secretary of State Marco Rubio . “He gets it solved.” Unbeknownst to the sweat-beaded dignitaries assembled for the president’s event, Trump of late had been discussing a new problem with his top diplomat: national security adviser Mike Waltz , whom he no longer trusted and who’d lost the confidence of much of the West Wing. The conundrum had been festering for weeks after Waltz inadvertently included a journalist on a Signal group chat to discuss a military strike in Yemen. Now it was no longer sustainable, people familiar with the matter said. Already this week, he’d determined Waltz should not travel with him to Michigan, w...