McMaster kept telling Potus. "No he couldn't do this or no Potus couldn't do that" when it came to the Iran deal.
McMaster wanted to make little deals, incremental 3 month moves.
Potus doesn't want the Iran deal. He wants it ended. Bolton will probably get that done and serve Potus's agenda in this regard well.
Better then McMaster who thought he was the guy who would tell Potus no and not be a yes man. Potus didn't want a yes man, he just wanted a man who was smart enough to get the deal done. McMaster, thought he was, "all that" Potus thought he was anything but.