It was almost 10 months between the Saturday Night Massacre and Nixon's resignation. The obvious problem is that Trump is far less rational than Richard Nixon ever was, and he has a slew of Republicans in Congress that will turn a blind eye to anything he does, right up to the point it looks like they are going to lose reelection.
2018 elections are 18 months away, but of course their low poll numbers would be apparent well before that.
