If Congress ever gets the guts to stand up to the President, they can override most of everything that he does. The reason why they don't is, their people won't elect them next time if they oppose what the people want >>> what the president does.
Well, yea; if the people elect Trump and congress decides to try to stop him then they won't be re-elected. Regardless, however, they do seem to be trying to stop him. A lot :/