In an unexpected decision that blindsided his own senior officials and signaled a concession to Turkey, U.S. President Donald Trump on Wednesday suggested he is preparing to pull all U.S. troops out of Syria, a move that experts said will seriously undermine America’s already weak hand in the war-torn nation. For Trump, it was the latest instance of conducting policy by tweet without forewarning, and it came even as key officials such as Syria special envoy James Jeffrey were signaling that U.S. policy was to stay in the country. The Defense Department would not confirm the withdrawal or give a timeline for bringing troops home.