His biggest legislation were set in motion in the beginning of his term when he had a house and a senate. A lot of other things were done via executive actions. Not much GOP could do, and the same is happening now. There is virtually almost nothing democrats can do to stop Trump's agenda.
GOP could not stand him, and their priority was always to torpedo his administration. Unfortunately, he spent big chunk of his political capital on Obamacare and lost house and senate as a result, giving birth to tea party movement.
What they will do is set upon mass rioting for another 4 years...I hope that I'm wrong about that, but I doubt it...The media will be there to encourage it with their hopelessly slanted reporting.