Except of course that if Trump loses most of them can only win if an overwhelming majority of the Trump voters also vote for them. In fact they probably need somewhere between 90 and 100% of his voters to have a chance. Throwing Trump under the bus pretty much seals their fate, since even a small percentage of Trump voters declining to vote for the guys who stabbed their candidate in the back will cause them to lose their election.
The only candidates who can get away with trashing their own party's leaders are people running in House districts that always vote one way in the general election.
I'll tell you this, though ... If I were living in Ohio there is no way in hell I'd vote against Portman just because he's calling for Trump to get out of the race. There is absolutely no upside to casting a vote for Trump while sitting on your hands and letting a Democrat win that Senate seat.
Because I'll tell you something right now: a Trump presidency and a Democratic Congress is probably the worst combination imaginable ... because you're going to find out quickly that Trump's brand of "conservative" is really nothing of the sort.