Trump once again shows he's a political savant. This was the obvious move for someone who cares more about power than doing the right thing: he delivered a campaign promise, he appears strong to his supporters, he gives congressional Republicans something they want and at the same time acquires a bargaining chip with Europe and China that he can cash in later. It takes four years to unwind, so there isn't even much damage and he can announce some new deal right before he's up for election. By dragging the decision out for a week he also distracted from any ongoing talk about Russia etc. Kind of a classic agency problem: this is good for him, bad for the rest of the world.