There's numbers that impact the long-term, and numbers that impact the short.
The immediate numbers that can effect Trump are GOP rank & file approval. If he's strong within them (he is), then he is immune to any immediate threats to his Presidency, legislation, or agenda. With strong rank & file numbers, the GOP establishment will never move against him, and he is essential immovable. The Dems of course, are completely impotent against him. He will last his term, unless they (GOP rank & file) turn against him. As of now, his support is still very strong there - in the mid 80's.
Then, there's the longer term. I too have seen his numbers slip amongst the Indies, and that (if it continues) bids him vulnerability in 2020 for re-election. Besides turning out one's base, nothing sways elections more than Independents. So he has a problem here, especially consider he barely squeaked-by in 2016, and I suspect the Dem base is going to be a bit more active due to anti-Trumpism.
So in essence, his popularity amongst the GOP will determine his intra-term fate; his popularity amongst the Indies will determine his inter-term fate. He has no immediate problems (yet), but he is looking at possible re-election problems.
That's my opinion.