Debate moderator Chris Wallace asked the Republican nominee if he would "absolutely accept the result of this election."

Donald Trump repeatedly insisted at Wednesday night's debate in Las Vegas that the presidential election is rigged, and refused to say that he would ultimately accept the results regardless of the outcome.

The candidate then doubled down on his claim that the election is rigged, a growing talking point at his recent campaign rallies, accusing the media of being biased against him, and saying there are "millions of people that are registered to vote that should not be registered to vote."

Trump also claimed the election is rigged because his Democratic rival, Hillary Clinton, "should not be allowed to run."

"She is guilty of a very, very serious crime," Trump said, adding a moment later that "I say it is rigged, because she should never, Chris, she should never have been allowed to run for the presidency based on what she did with emails and so many other things."

Wallace then noted the tradition of a "peaceful transition of power" after presidential elections. When Wallace asked if Trump would honor that tradition, Trump hedged.

"What I'm saying, I will tell you at the time," he said. "I will keep you in suspense."

Clinton responded, calling Trump's comments "horrifying."

"This is a mindset," Clinton said. "This is how Donald thinks. And it's funny but it's also really troubling. That is not the way our democracy works. 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."