Why did Trump bring on McMaster's? He was at odd's with Trump in many respects.
Trump has hired, and then fired, several people that have been head scratchers.
I chalk it up to a few things, some of which are Trump being a political novice and a vast majority of the deep state hold overs were Soebarkah, hate America first-ers who no doubt "advised" Trump on several people they knew would hurt Trump's agenda and put him at odds with his base.
Trump ≈ Non-Interventionist.
Bolton ≈ Interventionist.
Water ≠ Oil
Just couldn't work out in the long term.