LAS VEGAS - Republican candidate Donald Trump on Wednesday would not commit to accepting the outcome of the Nov 8 US presidential election if he loses, challenging a cornerstone of American democracy and sending shockwaves across the political spectrum.
Mr Trump's refusal, which his Democratic rival Hillary Clinton called "horrifying", was the standout remark of the their third and final debate and ratcheted up claims he has made for weeks that the election was rigged against him.
Asked by moderator Chris Wallace whether Mr Trump would not commit to a peaceful transition of power, the businessman-turned-politician replied: "What I'm saying is that I will tell you at the time. I'll keep you in suspense. Ok?"
Mr Trump's statement may appeal to his anti-establishment followers, but it was unlikely to reverse opinion polls that show him losing, including in key states that will decide the election.
"That is not the way our democracy works," Mrs Clinton said during the debate. "We've been around for 240 years. We've had free and fair elections. We've accepted the outcomes when we may not have liked them. And that is what must be expected of anyone standing on a debate stage during a general election."
Later, she told reporters: "What he said tonight is part of his whole effort to blame somebody else for where he is in his campaign."
A CNN/ORC snap poll said 52% thought Mrs Clinton, the former US secretary of state, won the debate while 39% said Mr Trump, making his first run at public office, was the victor.
Mexico's peso currency, seen as a measure of Mr Trump's prospects, rose to its highest level in six weeks at the end of the debate, suggesting growing investor confidence of a Clinton victory. Mr Trump has vowed to build a wall on the border with Mexico to keep out illegal immigrants and has said he would make Mexico pay for it.
Republicans voice concern
Mainstream Republicans were quick to denounce the comment. US senator Lindsey Graham, a former Republican presidential candidate who has never warmed to Mr Trump, said: "If he loses, it will not be because the system is 'rigged' but because he failed as a candidate."
Ben Carson, a retired neurosurgeon who also ran for the Republican presidential nomination and now supports Mr Trump, defended him.
He said Mr Trump's message was that "if there's some kind of obvious fraud going on, he's going to say something about it."
"He didn't say he wouldn't accept it," Mr Carson told Reuters. "He said he would evaluate it at the time."
Mr Trump's running mate, vice presidential nominee Mike Pence, said Mr Trump "will accept the outcome" because he is going to win.
But Republican strategist Ryan Williams found Mr Trump's statement "deeply concerning".
"You have to accept the results of the election unless there are grounds for a recount and at this point it does not appear that we're heading for a close election," he said.
'A nasty woman'
In a debate that for the first time focused more on policy than character, the two candidates nonetheless lashed out at each other.
Mr Trump, 70, called Mrs Clinton "such a nasty woman," accused her campaign of orchestrating a series of accusations by women who said the businessman made unwanted sexual advances and said that both she and President Barack Obama were behind disturbances at his rallies.
He said the Clinton Foundation was a criminal enterprise and as a result she should not have been allowed to seek the presidency.
Mrs Clinton, 68, said Mr Trump himself had incited violence, belittled women and posed a danger to the United States. She said Mr Trump, a former reality TV star, had in the past also complained that his show was unjustly denied a US television Emmy award.
"I should have gotten it," Mr Trump retorted.
Mr Trump said all of the stories of sexual misdeeds were "totally false" and suggested Mrs Clinton was behind the charges. He called her campaign "sleazy" and said, "Nobody has more respect for women than I do, nobody."
Mrs Clinton said the women came forward after Mr Trump said in the last debate he had never made unwanted advances on women. In a 2005 video, Mr Trump was recorded bragging about groping women against their will.
"Donald thinks belittling women makes him bigger. He goes after their dignity, their self-worth and I don't think there is a woman anywhere who doesn't know what that feels like," said Mrs Clinton, the first woman to win the nomination of a major US political party.
The two candidates also had a spirited exchange on abortion, gun rights and immigration during the showdown.
Mrs Clinton said she would raise taxes on the wealthy to help fund the US government's Social Security retirement program. She said Mr Trump, who Forbes says is worth $3.7 billion, would be paying higher taxes too unless he can get out of it.
"Such a nasty woman," Mr Trump said.
Mr Trump and Mrs Clinton battled sharply over the influence of Vladimir Putin, with Mrs Clinton calling Mr Trump the Russian president's puppet and Mr Trump charging Mr Putin had repeatedly outsmarted Mrs Clinton.
Mrs Clinton and Mr Trump walked straight to their podiums when they were introduced at the University of Nevada, Las Vegas, once again forgoing the traditional handshake as they did at the second debate last week in St Louis, Missouri. This time they did not shake hands at the end of the debate either.