The establishment republican’s have brought this upon themselves by refusing to work with the President.
I think you've hit the nail on the head. President Trump can't count on a unified republican congress; especially the senate side.
At this point the republicans are a very fracture party with 3 main factions; the establishment wing(GOPe), the socialist wing(RINO's), and the conservative wing (Freedom Caucus). Those 3 factions are in no way aligned so why even keep up with the pretense they are on one side.
I think Trump knows this all too well. As bad as the dem side is; at least they can be counted on to vote one way. I personally wish the republican party was one big conservative Freedom Caucus but we all know what happens when we wish in one hand and fill the other with something unpleasant but real; it's the one that gets filled.