The final US presidential debate produced the most jaw-dropping moment of the 2016 election cycle - one which raised the question of whether the Republican nominee will reject the election result if he loses on Nov 8.
About an hour into the 90-minute debate, Mr Donald Trump refused to commit himself to accepting the election result, saying only that he would "look at it at the time". When pressed on whether he would honour the tradition of a peaceful transition of power, Mr Trump said: "I'll keep you in suspense."
Democratic nominee Hillary Clinton Clinton called his answer "horrifying", saying that he was "talking down our democracy".
Experts said Mr Trump's unprecedented comments cast aspersions on the US democratic process even before a single vote was cast. To the world, it "looks like a breakdown of our democratic process", said presidential historian Douglas Brinkley on CNN.
Mr Trump's answer overshadowed what had been his best debate performance and one of the more substantive clashes between the two candidates on issues such as the economy, immigration policy and the nomination of Supreme Court justices.
Mr Trump also attracted flak for referring to Mrs Clinton as a "nasty woman". When Mrs Clinton said that she would raise taxes on the wealthy to help fund social welfare programmes and that Mr Trump would end up paying higher taxes too unless he could get out of it, Mr Trump said: "Such a nasty woman."
Calling for tougher security at the Mexican border, Mr Trump also hit a raw nerve with Hispanic voters when he said he wanted to keep out major drug dealers, adding: "We have some bad hombres here and we're going to get them out." Hombres is Spanish for men.
Mr Trump appeared to have lost the debate, held at the University of Nevada Las Vegas. A CNN/ORC poll gave Mrs Clinton a 13 percentage point win - 52 per cent to 39 per cent - while YouGov's online poll showed her winning by 10 points.
But Mr Trump touted a Rasmussen Reports poll in the morning showing that he is ahead among likely voters by 43 per cent to Mrs Clinton's 40 per cent.
With less than three weeks to the election, Mr Trump has been trailing in nearly all opinion polls and telling supporters that the election is rigged against him.
Yesterday, his campaign manager, Ms Kellyanne Conway, said it was too early to say whether voting irregularities could make the difference between winning and losing.
"He's saying that until the results are actually known, certified and verified, he's not going to concede the election," she said on a morning talk show. She added: "He respects the principles of democracy. It's just that he can't say what's going to happen."