Personally, I think he's being overly pessimistic about the Senate (not outside the realm of possibility, but I don't believe it's as probable as he makes it out to be). However, I do agree with his concerns over Trump's comments. I was actually leaning towards hopping on the Trump train until he said that. All the good will he had built up with me was destroyed in one fell swoop by that single remark.
If it ever gets to the point where such a bill is placed before him, and he signs it, that will be the end of any 2020 aspirations he may hold. There's no way he holds onto his base after that.