Just because I can't recall it all, here's a few questions.
What exactly did Trump promise to do?
How likely is it he can accomplish this?
How will those who voted him in react if it turns out he can't fulfill these promises?
He promised some things that he can do almost unilaterally:
Overturn Obama executive orders relating to climate change, and I think he can get us out of the Paris and Iran deals without congress, but somebody correct me if I'm wrong on that.
Other things he promised (repealing Obamacare) need the help of congress, but now that they control everything, it's very likely.
He can also nominate SCOTUS justices that will be strongly anti-abortion and anti-any-gun-laws-whatsoever. The democrats can filibuster the nominations, but Republicans can also nuke the filibuster to get them appointed. And it's very likely that Trump could be appointing two justices, and shift the power back to conservatives dramatically.
Other things (build the wall, deport millions of undocumented immigrants) need congress, and are still going to be difficult without large republican support (the same republicans who avoided supporting Trump). But if they fall in line, he could literally sign a bill that says we're going to build a wall and divert massive resources to locating and deporting immigrants. Guess what would be the check on some of those laws? The fucking SCOTUS. Dammit.