Donald Trump's allies are struggling to defend his refusal at the final presidential debate to say he will honour the results of the November election should he lose.
Condemnation of his stance has come from Republicans and Democrats alike.
Sean Spicer, the chief strategist of the Republican National Committee, which is supplying much of the Trump campaign's get-out-the-vote and voter outreach efforts, said the national party would "respect the will of the people."
"I cannot speak for what he thinks," Spicer said.
South Carolina Senator Lindsey Graham said "Mr Trump is doing the party and the country a great disservice" by suggesting the election is rigged, while Arionza Senator Jeff Flake called the New York billionaire's statements "beyond the pale".
After spending the past few weeks claiming without evidence that the November election will be "rigged" in favour of Democratic nominee Hillary Clinton, Trump was asked directly by Fox News anchor and debate moderator Chris Wallace if he would concede should he lose.
"I will look at it at the time," Trump said. When pressed moments later, Trump added: "What I'm saying is that I will tell you at the time. I will keep you in suspense."
Clinton called Trump's comments "horrifying".
Billionaire Mark Cuban, one of Clinton's top supporters, called Trump's words "a slap in the face of every American in the history of this country, the constitution and our democracy".
"That's what we're proud of," he said. "So, for him to question that, that's disqualifying."
Trump's remarkable comments came just hours after his running mate, Indiana Governor Mike Pence, said on CNN "that we'll certainly accept the outcome of this election".
Trump's daughter Ivanka, arguably his most influential adviser, also said earlier on Wednesday her father would "do the right thing" when she was asked if he would concede after a defeat.
The debate answer left his own team scrambling in the aftermath. Kellyanne Conway, his campaign manager, at first responded to questions about the comment by saying he "would accept the results because he'll win the election".
"So, you know, absent widespread fraud and irregularities, then, we'll see," Conway said. "What he's saying is we have to see what happens."
She later rejected the outcry over Trump's comment, saying it's "not fair" to suggest Trump is undermining the prospects of a peaceful transfer of power.
"You've got to listen to everything he said," she argued.
"Al Gore did not accept the results of the elections and he said he would. He actually conceded to George W. Bush on election night in 2000 and then called and retracted his concession."
Former New York City Mayor Rudy Giuliani, another of Trump's top allies, said the Republican nominee had good reason to be suspicious about potential fraud.
"There are indications of a lot of fraud around by the Clintons," Giuliani said.
