Tom, I think the way to cut Trump off at the knees is in three words:
No, You Can't.
He doesn't take well to being told no. From the beginning of his administration, he's held the view that he can rule by fiat. Slowly but surely, he's been disabused of that notion, though in terms of some foreign operations, the president by definition has considerable latitude. Trump has used that in unilaterally ordering the pull-out from Syria, with proposed withdrawals from Afghanistan and possibly South Korea in the offing.
Domestic policy, however, is a different matter, as are other operational processes, made purposefully so by the Constitution. As of 3 January, 2019, he will face a strongly Democratic House of Representatives which will resist if not flat-out oppose a great number of his goals, with "The Wall" at or near the top of that list. Add to that, Senate Republicans are slowly (more like glacially!) but surely coming to grips with the dangerous nature which this administration represents, and as Trump's actions become more extreme and erratic, may finally be willing to confront him about it. This is an especially important job for Congress in general, as "the adults in the room," being Mattis and Kelly have either left or are leaving.
The key word here is: FRUSTRATION. Frustrate Trump enough, cut off his wiggle room, force him to confront the realities, legal and otherwise, of his position as president, and he may finally figure out that the position isn't worth the toll. It's a nice theory. It'd be nicer if it actually worked.
I'm with Loren on this. If the newly elected mid term people band together and continually hammer Trump and his ideas with NO, YOU CAN'T it might sink in with many after repeated court actions that we will not stand for this. Those supporters who want to survive politically will switch sides once they see that Trumpism is a sinking ship. You cannot continually tie your future to something that has no future.
The unfortunate thing is that this will probably take another 2 years.