Clinton leads Trump by 12 points among likely voters nationwide in a four-way contest
Trailing in national polls and in key battleground states just three weeks before Election Day November 8, Trump came out swinging on the campaign trail, accusing Clinton of colluding with US authorities to cover up misconduct regarding her private email system and denouncing it as "one of the great miscarriages of justice" in US history.
Trump, whose campaign has been reeling in the face of lewd comments about women and accusations of sexual assault, has doubled down on claims of massive voter fraud in 2016, despite denials from within his own party.
And his team has deployed his wife Melania in a media blitz to try to tamp down the furor over the allegations, with interviews airing late Monday on CNN and early Tuesday on Fox News.
"Those words, they were offensive to me and they were inappropriate. And he apologized to me. And I accept his apology. And we are moving on," Trump told Fox, in an excerpt released by the network.
A firestorm erupted earlier this month when a 2005 video was made public and caught Trump saying lewd things about women, in a mostly off-camera conversation with host Billy Bush of the show "Access Hollywood."
Melania Trump told CNN that she felt her husband had been "egged on by the host to say dirty and bad stuff."
The Republican nominee takes the stage Wednesday with his Democratic rival Hillary Clinton in their final debate before voters make their choice.
Trump unleashed a litany of complaints recently about the nation's election system, and also blamed the media for his woes, raising concerns about possible unrest should he lose.
He let loose again Monday at a rally in Green Bay, Wisconsin.
"Voter fraud is very, very common," he told a fired up crowd, who at various times broke into chants of "Lock her up!" "Tell the truth!" and "CNN sucks!"
"This is a rigged election folks," he said. "And the media's trying to rig the election by giving credence... to false stories that have no validity," he added.
"They want to poison the minds of the voters."
Trump also accused Clinton of colluding with US authorities by seeking to pressure the FBI to alter its findings in a probe of Clinton's use of private servers while she was secretary of state.
Federal Bureau of Investigation documents released Monday showed a senior State Department official, undersecretary of state Patrick Kennedy, had asked the FBI to declassify or lower the classification of one Clinton email that had been rated secret.
Trump said the State Department official made the request for altering classification "as part of a 'quid pro quo.'"
"We're witnessing a criminal enterprise" at work, he said of the Clinton campaign.
"This is felony corruption by any standard."
Clinton leads Trump by 12 points, 50 percent to 38 percent, among likely voters nationwide in a four-way contest with third-party candidates, a Monmouth University poll showed.
Meanwhile, a survey from Quinnipiac University had Clinton leading in several key swing states -- Colorado, Florida and Pennsylvania -- and tied with Trump in Ohio.
A CNN poll puts Trump ahead by four points in Ohio, but gives Clinton a slight lead in battlegrounds North Carolina and Nevada.
Her leads in key states correspond to her advantage of 6.4 percentage points in an average of recent national polls given by RealClearPolitics.
The polls indicate that the allegations swirling around Trump have taken their toll. Monmouth found that six in 10 voters believe he made unwanted sexual advances towards women -- claims he vehemently denies.
Trump's running mate Mike Pence sought to ease tensions, insisting his camp would accept defeat if voters reject the Republican ticket at the polls.
"We will absolutely accept the results of the election," he told CBS Sunday.
Ohio Secretary of State Jon Husted, a Republican who oversees election operations in his state, insisted that Trump was being "irresponsible," after the nominee tweeted a warning Monday about "large scale voter fraud" in the US election.
"If there is a systemic problem, please identify it. Don't just make an allegation on Twitter. Tell me," Husted said on CNN.
For Clinton's campaign manager Robby Mook, Trump is "desperately trying to shift attention from his own disastrous campaign."
"He knows he's losing and he's trying to blame that on the system. This is what losers do," Mook said during a press call on Monday.
Clinton was lying low Monday, prepping for the final debate.
"She is trying to avoid issues for the next 22 days in the hopes that this will just end up being about Mr. Trump," his campaign manager Kellyanne Conway told CNN Monday outside of Trump Tower in New York.