“THIS IS having nothing to do with me but having to do with the future of our country,” Donald Trump said Thursday. That statement could have been the punch line to a self-deprecating joke at that night’s Al Smith charity dinner; Mr. Trump’s ego and thin skin have been defining elements of his campaign. In fact, Mr. Trump spoke these words at a rally earlier in the day, attempting to explain his inexplicable refusal to commit to abiding by next month’s election results.

In a way, he was right. Mr. Trump is threatening to damage much more than his campaign by mocking the peaceful transition of power. “I will totally accept the results of this great and historic presidential election — if I win,” he declared, before saying that he reserves the right to challenge “questionable” results. Mr. Trump would, of course, define “questionable.”

Thus has Mr. Trump issued yet another challenge to those Republicans who aspire to play key roles in the nation’s political life after the election. The Post’s Philip Rucker and Robert Costa report: “The immediate responses from GOP officials were divergent and vague, with no clear strategy on how to handle Trump’s threat.” How about telling the truth?

Republican National Committee Chairman Reince Priebus, among others, attempted to play down Mr. Trump’s conspiracy-mongering, insisting that the GOP nominee is simply reserving the right to a recount in a close result. Not so: As if to correct Mr. Priebus, Mr. Trump declared Friday that “the whole deal is rigged.” Former New York mayor Rudy Giuliani offered a taste of the accusations that would emanate from the Trump camp, insisting without evidence that Philadelphia Democrats will “steal a lot more than 50 votes in Philadelphia. I guarantee you of that. And I’ll tell you how they will do it — they’ll bus people in who will vote dead people’s names four, five, six times.”

A number of Republican National Committee members, meanwhile, have hyped the notion that the election will be riddled with fraud, repeating, for example, unsubstantiated claims that “illegals” will vote in droves.

House Speaker Paul D. Ryan’s office has said he is “fully confident the states will carry out this election with integrity,” and Politico reported that Mr. Ryan (R-Wis.) and Senate Majority Leader Mitch McConnell (R-Ky.) would likely step in after the election should Mr. Trump refuse to accept the results. But their nominee is doing damage now; polls show the vast majority of Republicans believe a Hillary Clinton victory would be due to fraud. Their leaders must tell them otherwise, with much more force.

A few Republicans have found their way to the right tone. Sen. John McCain (Ariz.) said, “I didn’t like the outcome of the 2008 election. But I had a duty to concede.” Sens. Kelly Ayotte (N.H.), Patrick J. Toomey (Pa.) and Ron Johnson (Wis.) have each issued criticisms of varying severity.

But the condemnation should not be isolated. It should be deafening. Any Republican who wants to emerge from this election with a shred of integrity must speak up.