Note that Ben Sasse isn't a never Trumper. Frankly Ben Sasse has been one of the most disappointing Senators. While he has talked about Constitutional principles and the value of the Separation of Powers he's gone along with Trump several times including voting for Trump's use of Emergency powers to bypass Congress.
I think McSally, Gardner, and Collins are all very vulnerable. It wouldn't surprise me if all three get beaten pretty badly in 2020, especially Gardner and Collins. I'm not ready to make predictions about the others, or about 2022. Not yet. I will predict that Democrats will take back the Senate in 2020, but a lot will depend on who gets the nod as the presidential nominee. Back in '76, Democrats should have beaten the GOP like a drum in the Congressional races, both the House and the Senate. They didn't. Why? They (I was an independent voter at the time) nominated a weak choice at the head of the ticket, Jimmy Carter. So weak that Ford had a decent chance of winning (and he was a decent man, in my opinion, the kind you can't locate in today's GOP), but Watergate, his pardon of Nixon, and his stupid comment about the Iron Curtain sunk his campaign. Carter was a lousy candidate and ended up being a lousy president, again, in my opinion. He's been a far better former president.
