Las Vegas - Donald Trump's allies struggled late on Wednesday to defend his refusal at the final presidential debate to say he will honour the results of the November election should he lose, with condemnation arriving from both 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 Sen. Lindsey Graham said in a statement that "Mr. Trump is doing the party and the country a great disservice" by suggesting the election is rigged, while Arionza Sen. Jeff Flake called the New York billionaire's statements "beyond the pale."'Horrifying' commentsAfter 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 to Clinton."I will look at it at the time," Trump said. When pressed moments later, Trump added simply: "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." And Trump's daughter Ivanka, arguably his most influential adviser, said earlier on Wednesday that her father would "do the right thing" when she was asked if he would concede after a defeat in November.No proofThe debate answer left his own team scrambling in the aftermath of the debate. 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."Gore pulled back his concession only after updated vote count results in Florida showed the state too close to call, throwing the outcome of the election into doubt. When the US Supreme Court later halted a recount, leaving Bush ahead in Florida and giving him the election, Gore conceded and asked the country to accept Bush as the nation's next leader.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.In fact, there is no proof that voter fraud is a widespread problem in the US. A study by a Loyola Law School professor found that out of 1 billion votes cast in all American elections between 2000 and 2014, there were only 31 known cases of impersonation fraud.