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Donald Trump's stunning refusal to say whether he will accept the outcome of the election has created chasms in an already fractured Republican Party — drawing criticism from congressmen, including prior presidential candidates.

"I didn’t like the outcome of the 2008 election,” Arizona Sen. John McCain, the Republican nominee that year, said in a statement Thursday. “But I had a duty to concede, and I did so without reluctance. 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.”

"I don’t know who’s going to win the presidential election. I do know that in every previous election, the loser congratulates the winner and calls them, 'my president.' That’s not just the Republican way or the Democratic way. It’s the American way," McCain added.

Trump didn't give a direct answer when asked during Wednesday's final presidential debate whether he would accept the results of the election, which he has repeatedly claimed is rigged. Instead, he replied that he would "keep you in suspense."

"I will look at it at the time. I'm not looking at anything now. I'll look at it at the time," Trump told moderator Fox News' Chris Wallace.

On Thursday, in his first remarks since the debate, Trump clarified that he would indeed accept the results — if they're in his favor.

"Ladies and gentlemen, I want to make a major announcement today," Trump told a rally in Delaware, Ohio. "I would like to promise and pledge to all of my voters and supporters and to all of the people of the United States that I will totally accept the results of this great and historic presidential election — if I win."

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Related: Election Officials Say 'Rigged' Election Unlikely

If Trump loses and doesn't concede, it would break from an American tradition dating back to the Civil War — and a number of Republicans were swift to condemn him for it.

Trump "saying that he might not accept election results is beyond the pale," Arizona Sen. Jeff Flake tweeted.

.@realDonaldTrump saying that he might not accept election results is beyond the pale — Jeff Flake (@JeffFlake) October 20, 2016

South Carolina Sen. Lindsey Graham said in a statement that he, like most Americans, has "confidence in our democracy and election system."

“During this debate Mr. Trump is doing the party and country a great disservice by continuing to suggest the outcome of this election is out of his hands and 'rigged' against him. If he loses, it will not be because the system is 'rigged' but because he failed as a candidate." Graham said.

New Hampshire Sen. Kelly Ayotte, a former attorney general, urged Trump to accept the outcome.

"This is important. I don't believe that there's a rigged election system. If there are allegations that need to be investigated, they'll be investigated," she said.

Even controversial Maine Gov. Paul LePage chimed in, telling WGAN radio of Portland: "Not accepting the results, I think, is just a stupid comment."

Trump's unprecedented remark is the latest in a string of controversies that have prompted harsh responses from members of his own party. Most recently, many Republicans distanced themselves from the candidate following sexual assault allegations against him and the release of a 2005 tape in which Trump, using lewd language, described groping women.

Related: Melania Trump: Donald Was 'Egged On' to Make Lewd Comments

Even for a candidate who has been full of surprises, this was jaw-dropping, experts said.

"It wasn’t just what he said that was shocking, it was the way he said it. There was a casual contempt in Donald Trump’s voice for 225 years of American political tradition," MSNBC analyst and Huffington Post global editorial director Howard Fineman said.

Florida Republican Rep. Carlos Curbelo slammed Trump for suggesting he would break such a central tenet of American democracy.

Peaceful transfer of power & acceptance of election results is fundamental to our democracy & Constitution. This cannot be undermined ever. — Carlos Curbelo (@carloslcurbelo) October 20, 2016

"Peaceful transfer of power & acceptance of election results is fundamental to our democracy & Constitution. This cannot be undermined ever," he tweeted.

The response also went against what Trump's own running mate Mike Pence, daughter Ivanka, and campaign manager Kellyanne Conway have said.

Related: Ivanka Trump: My Father Will 'Accept the Outcome Either Way'

"Donald Trump will accept the result of the election because he will win the election, so it will be easy to accept," Conway said after the debate.

Ben Ginsberg, former Republican National Convention counsel, told MSNBC Trump's remarks "will have exactly the opposite effect of what they intended."

"In fact, what he’s done is give the Democrats a terrific get-out-the-vote mechanism to make more Democrats come out who are not naturally enthusiastic about Hillary, and it will actually increase Democratic turnout," Ginsberg said.