Arizona Republican Sen. John McCain said it was imperative politicians “respect the decision of the majority . . . especially when we disagree with it.” (Ross D. Franklin/AP)

Prominent Republicans in tough reelection battles spent Thursday blasting Donald Trump for refusing to promise that he would respect the results of the presidential election if he loses.

“There have been irregularities in our elections, sometimes even fraud, but never to an extent that it affected the outcome,” said GOP Sen. John McCain, who is up for reelection in Arizona, where some polls show Clinton with an edge in the traditionally red state, even though the senator has a big edge on his own rival.

“We should all be proud of that, and respect the decision of the majority even when we disagree with it. Especially when we disagree with it.”

McCain joined other Republican senators from blue states facing tough reelection bids in condemning the remarks, including Sens. Kelly Ayotte (N.H.), Rob Portman (Ohio), and Ron Johnson (Wis.).

But as of midday, House Speaker Paul D. Ryan (Wis.) and Senate Majority Leader Mitch McConnell (Ky.) — whose own GOP majorities are at stake because of Trump’s unpopularity — had not commented on the latest statement from Trump about the election’s legitimacy.

Ryan’s office pushed back earlier this week against allegations of a “rigged” election, when spokeswoman AshLee Strong said: “Our democracy relies on confidence in election results, and the speaker is fully confident the states will carry out this election with integrity.”

The Republican backlash was sparked by an exchange during Wednesday night’s final presidential debate, in which Trump repeatedly refused to say he would accept the results of the election, despite pledges to do so from his running mate, Indiana Gov. Mike Pence, and daughter, Ivanka Trump.

Republican presidential nominee Donald Trump said, "I'll keep you in suspense," when answering a question about the tradition of accepting the results of presidential elections. (The Washington Post)

“I will tell you at the time. I’ll keep you in suspense,” Trump told moderator Chris Wallace, a response Hillary Clinton called “horrifying.”

Trump clarified his position during a campaign rally Thursday, in which he told supporters that he would “totally accept the results of this great and historic presidential election — if I win.”

He added that he would also “accept a clear election result,” but “reserve my right to contest or file a legal challenge in the case of a questionable result.” Trump did not define where he considered the line between a clear and a questionable result to be.

Republican presidential nominee said he will accept the results of the election if he wins, at a rally on Oct. 20 in Delaware, Ohio. (The Washington Post)

The latest broadside — which was roundly criticized by conservatives across the GOP — is likely to cause even more headaches for down-ballot Republicans, who already fear mass Republican defections because of Trump’s polarizing nature and unconventional stances.

McCain knows something about conceding a presidential election — he had to do as the GOP nominee in 2008, to President Obama. He noted in a statement Thursday that he “didn’t like the outcome” of that election, but “had a duty to concede, and I did so.”

“A concession isn’t just an exercise in graciousness. It is an act of respect for the will of the American people, a respect that is every American leader’s first responsibility,” McCain said.

Other embattled Republicans pointed out that Trump needed to respect a process that has safeguards in place to examine and correct for uncommon irregularities.

“The voters are going to decide this election, and Donald Trump needs to accept the outcome,” said Ayotte, who served as New Hampshire’s attorney general and has a slight lead this year against Gov. Maggie Hassan (D). “If there are reports that need to be investigated, they will be, as I used to do as attorney general.”

Portman also expressed “full faith” that Ohio state officials could sort out any allegations of impropriety on Election Day “to ensure the integrity of the election,” in a statement Thursday. Portman is well ahead of his Democratic rival in a state that is very competitive at the presidential level.

A campaign spokesman for Johnson also said in a statement Thursday that Johnson “believes we need to respect the results on Election Day.” Johnson is trailing former senator Russ Feingold (D) in his reelection contest in the Badger State with Clinton ahead there.

Sen. Roy Blunt (R-Mo.) took a slightly different approach, using the controversy as an opportunity to criticize his Democratic opponent Jason Kander, who currently serves as Missouri’s secretary of state.

“I have faith in the electoral system across the country, but it is still important to watch for the type of conduct that should not happen on Election Day,” Blunt said in a statement. “I don’t have faith in Missouri’s chief election official Jason Kander because of multiple ballot blunders, judicial rulings, and court mandates that required two do-over elections in recent months.”

Trump has spent the past several days charging that the election is “rigged” to help Clinton, casting a long shadow of doubt on the sanctity of the American elections process and its potential outcome.

Right now, Trump is lagging behind Clinton in almost every national poll.