David Jackson

USA TODAY

LAS VEGAS — The presidential candidates ended their series of three debates with one candidate questioning the very legitimacy of the election should he lose.

Donald Trump on Thursday mocked critics of his refusal during the debate to commit to honoring the election outcome, joking to supporters in Ohio that he will "totally accept the results of this great and historic presidential election — if I win."

Maintaining his claims that the Hillary Clinton campaign and the "dishonest media" are conspiring to "rig" the election against him through vote fraud and biased reporting, Trump told supporters in Delaware, Ohio, that "we want fairness in the election. ... Don't be naïve, folks. Don't be naïve."

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Similar comments by Trump during Wednesday's debate drew criticism from members of both political parties, who noted that the Republican nominee has no evidence to back his claims of voter fraud, especially before Election Day on Nov. 8.

"That was the big shocker of the evening," Clinton's running mate, Virginia Sen. Tim Kaine, told CBS This Morning the day after the candidates faced off in their third and final debate in Las Vegas.

Trump is claiming a rigged election because "he knows that he's losing," Kaine said, and "he just doesn't know how to take responsibility."

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Trump aides said he was referring to real concerns about voter fraud as well as what they called biased news coverage against the New York businessman.

"He’s saying that until the results are actually known, certified and verified, he’s not going to concede an election," Trump campaign manager Kellyanne Conway said on ABC's Good Morning America. "He just doesn’t know what will happen."

In Ohio, Trump told supporters that "the bottom line is we're going to win." Trump also said that he would "accept a clear election result," but he would also "reserve my right to contest or file a legal challenge in the case of a questionable result."

The key moment in Wednesday's debate came when moderator Chris Wallace asked Trump about his rigging allegations, and whether he would accept the results of the election.

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"I will look at it at the time," Trump replied, citing the "corrupt media," claims — without evidence — that millions of people are registered to vote who shouldn't be, and his contention that Clinton "shouldn't be allowed to run" for president "based on what she did with emails and so many other things."

Asked again about the American tradition in which the loser of an election concedes to the winner in order to effect a peaceful transfer of power, Trump said: "What I'm saying is that I will tell you at the time. I'll keep you in suspense. OK?"

Clinton called Trump's answer "horrifying" and added that "every time Donald thinks things are not going in his direction, he claims whatever it is, is rigged against him."

Several sharp personal exchanges punctuated a debate otherwise devoted to issues like the Supreme Court, immigration and foreign policy.

When Clinton knocked Trump's efforts to avoid paying federal income tax, the Republican nominee interjected with the comment "such a nasty woman."

Trump also called his Democratic rival a "liar," while Clinton accused him of being a potential "puppet" for Russian President Vladimir Putin; she approvingly cited her former primary rival Bernie Sanders' claim that Trump is "the most dangerous person to run for president in the modern history of America."

In the wake of the last debate of this cycle, a number of Republicans also criticized Trump's lack of commitment to respect the election. Sen. Jeff Flake, R-Ariz., a frequent critic of Trump, tweeted that the GOP nominee "saying that he might not accept election results is beyond the pale."

Sen. John McCain, R-Ariz., the party's 2008 presidential nominee, did not mention Trump by name, but he made his point clear in a statement saying that all Americans "should be confident" in the integrity of U.S. elections. While noting that he did not like losing the 2008 election to Barack Obama, McCain said he had a duty and responsibility to concede the election to the new president and did so.

"I don’t know who’s going to win the presidential election," McCain said. "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."

Democratic strategist Lis Smith said Trump blew whatever chance he had to change the trajectory of the race by offering "a really dark and dystopian view of America" during the debate.

Clinton had her best debate performance yet, Smith said, and landed "some real punches — calling Trump Putin's puppet, noting his 'beautiful hotel' (in Las Vegas) was constructed with Chinese steel, and contrasting how she was in the Situation Room during the bin Laden raid while he was judging Celebrity Apprentice."

Clinton's performance in all three debates got a social media shout-out from President Obama, who tweeted: "Outstanding 3 for 3 debate sweep for @HillaryClinton! Nobody has ever been more prepared to be @POTUS."

The former secretary of State entered the debate with leads over Trump in polls, both nationally and in the states likely to decide who wins the Electoral College.

Republican pollster Frank Luntz, who conducted a focus group during the debate, said "it's hard to see that either candidate was able to win voters leaning to their opponent." Luntz also said Trump's implicit threat to protest the election was a turn-off.

"Voters resented his refusal to accept their verdict," Luntz said. "Frankly, voters want this election over, and anything that draws it out will be rejected."

Many Republicans doubt that Trump can rally in the last 19 days of the election.

Matt Mackowiak, a Republican consultant based in Texas, said Trump's answer to the election acceptance question "is overwhelming what would have been a clear debate victory for him."

Sarah Isgur Flores, another GOP strategist based in Texas, said the Republican nominee "once again gave away the game by refusing to say he would accept the results of the election," and that Clinton will win the election.

Aaron Kall, director of debate at the University of Michigan, said Trump's refusal to commit to accepting the election's outcome is likely to undermine his debate performance overall.

"This major error will dominate the news cycle for the next several days," Kall said, "while continuing to expose the divide that exists between the Trump campaign and Republican establishment."