Here is another indication of how bad the November bloodbath will be for Trump if he is the nominee. Every time there is a bruising GOP primary, there are always people who emerge with hurt feelings, but the RNC, NRSC, and NRCC always get the message out quickly that everyone needs to present a united front in favor of the nominee. In some very rare circumstances, where a very blue state Senator is running for re-election, an ad carefully distancing the Senator from a Republican nominee gets greenlit, but those are by far the exception rather than the rule.
I really more or less expected that to be true of Trump, in spite of everything. Most elected Republicans are creatures of the party, after all, and tend to fall in line when ordered to do so. Apparently, not so much, as McConnell has already given the carte blanche go ahead to run anti-Trump general election ads for any candidate who feels the need to do so.
Mr. McConnell has begun preparing senators for the prospect of a Trump nomination, assuring them that, if it threatened to harm them in the general election, they could run negative ads about Mr. Trump to create space between him and Republican senators seeking re-election. Mr. McConnell has raised the possibility of treating Mr. Trump’s loss as a given and describing a Republican Senate to voters as a necessary check on a President Hillary Clinton, according to senators at the lunches.
He has reminded colleagues of his own 1996 re-election campaign, when he won comfortably amid President Bill Clinton’s easy re-election. Of Mr. Trump, Mr. McConnell has said, “We’ll drop him like a hot rock,” according to his colleagues.
Trump's supporters are of the delusional belief that none of this will matter. Certainly, the lack of support from a single Senator hasn't prevented Trump from accumulating about 35% of the Republican vote. But if he runs in November with even 10 or 15 Senators from his own party are running ads against him, he is going to have no chance to accumulate independent votes he needs to win.
It's one thing for Trump to be opposed by milquetoasts like Mark Kirk - but it's another thing for him to be opposed by people like Ben Sasse, which he almost certainly will do.
Remember, the media scrutiny Trump will face when he's facing a Democrat will be qualitatively different from the scrutiny he is facing now. "Trump is opposed by an unprecedented number of Senators from his own party" is a message that lands with general election voters, and it should. Trump and his unshakeable mob might be enough to win the primary, but they will get slaughtered in the general.