Assad (with Russian help was winning albeit slowly). The U.S. literally has “boots on the ground” training “Syrian Rebels”. Why would the Russians just bend over and accept a new leader who is an unknown? Assad is doing what they want him to do. Sorry, but Trumps move is looking dumber and dumber to all but the Neo-Cons, Leftists, and cognitively-challenged Right.
Because it's not working out very well. Especially considering recent developments.
Trump's move only looks dumb to dumb people.