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 :/
If Congress is going to find substantiated proof that nothing bad will happen. It would be much worse if Lawmakers will find evidence and keep silence about it. Let me remind you that the investigation is carried out into the relations with Russia, and this is the main enemy of the security of America.