There is no standard of proof. If you’re hated by enough of the right people, you’re done. That’s it. In a time of unlimited corruption counting on people to act honorably is a fool’s game.
And Trump at this point is the head fool. You don’t announce something like the withdrawal from Syria and all that that entails only to walk it back 10 days later because someone threatened you. In fact, Trump’s best, and frankly, only course of action now is to go on the offensive.