Republican candidate Donald Trump said on Friday that he continues to believe the Nov. 8 election is "rigged" against him, a message that has resonated with members of his party, a new Reuters/Ipsos poll shows.
Trump has been coy about whether he will accept the results of the election should Democratic rival Hillary Clinton beat him.
Both candidates spent Friday in battleground states, where the vote could swing either way. Trump, 70, was in North Carolina and Pennsylvania, while Clinton, 68, campaigned in Ohio.
A new Reuters/Ipsos poll showed only half of Republicans would accept Clinton as their president, and nearly 70 percent of them said a Clinton victory would be because of illegal voting or vote rigging.
"Remember folks, it's a rigged system," Trump told a rally in Johnstown, Pennsylvania. "That's why you've got to get out and vote, you've got to watch. Because this system is totally rigged."
Trump's crowd chanted "Lock her up!" after he declared Clinton a "corrupt globalist," a reference to campaign documents released by WikiLeaks.
After the chant went around the room for several seconds, Trump responded, "Don't worry, that whole thing will be looked into."
The New York businessman's assertion that the election is being rigged and his refusal to commit to accepting the outcome of the election if he loses has challenged a cornerstone of American democracy and outraged Democrats and many Republicans.
Asked if he would commit to a peaceful transition of power during Wednesday's debate, Trump replied: "What I'm saying is that I will tell you at the time. I'll keep you in suspense. OK?"
In Ohio on Friday, Clinton called his refusal unprecedented. "Now make no mistake: by doing that, he is threatening our democracy," she told a rally in Cleveland.
"But we know in our country the difference between leadership and dictatorship, right? And the peaceful transition of power is one of the things that sets us apart," Clinton said.
Trump, who has been lagging in opinion polls, has offered no widely accepted evidence to back up his claims of vote-rigging. Numerous studies have shown that the U.S. election system, which is run by the states, is sound.
Clinton's lead over Trump in national opinion polls has grown in recent weeks. An average of polls by RealClearPolitics shows her currently 6.3 percentage points ahead at 48.5 percent support to Trump's 42.2 percent.
Trump told an earlier rally in Fletcher, North Carolina, that he wanted to have no regrets about whether he worked hard enough to win the election, and urged followers to get out to vote.
"Win, lose or draw - and I’m almost sure if the people come out, we’re going to win - I will be happy with myself," he said. "We have to work, we have to get everybody out there.”
(Additional reporting by Doina Chiacu, Ginger Gibson and Susan Heavey; Writing by Alistair Bell and Roberta Rampton; Editing by Frances Kerry and Jonathan Oatis)