Donald Trump has said a cloud of investigation would follow a victorious Hillary Clinton into the White House, evoking the bitter impeachment battle of the 1990s in a closing campaign argument meant to bring wayward Republican voters home.
For her part, Democrat presidential candidate Mrs Clinton and her allies, led by President Barack Obama, told voters to get serious about the dangers of Mr Trump.
As polls show Mr Trump closing in on Mrs Clinton in key battleground states, her campaign is rushing to shore up support in some long-standing Democratic strongholds. That includes the campaign's Michigan firewall - a remarkable situation for a candidate who looked to be cruising to an easy win just a week ago.
Mrs Clinton's shrunken lead has given Mr Trump's campaign a glimmer of hope, one he is trying to broaden into a breakthrough before time runs out, zeroing in on questions of Mrs Clinton's trustworthiness and a new FBI review of an aide's emails.
The attack is aimed at appealing to moderate Republicans and independents who have been the holdouts of his campaign, turned off by his behaviour but equally repelled by the possible return of the Clintons.
"Here we go again with the Clintons - you remember the impeachment and the problems," Mr Trump said at a rally in Jacksonville, Florida.
"That's not what we need in our country, folks. We need someone who is ready to go to work."
Mrs Clinton and friends, meanwhile, are seeking to keep the spotlight on Mr Trump, charging that his temperament and his disparaging comments about women and minorities make him unfit for office.
"He has spent this entire campaign offering a dog whistle to his most hateful supporters," Mrs Clinton said, singling out Mr Trump's endorsement from the official newspaper of the Ku Klux Klan and noting he has retweeted messages from white supremacists.
"This has never happened to a nominee of a major party.
"If Donald Trump were to win this election we would have a commander in chief who is completely out of his depth and whose ideas are incredibly dangerous," she said at Pitt Community College outside of Greenville, North Carolina.
Mrs Clinton campaigned later with former primary opponent Bernie Sanders and pop star Pharrell Williams in Raleigh, where she warned that Mr Trump's election risked "normalising discrimination".
Also in battleground North Carolina, Mr Trump delivered a defence-related speech at a night-time rally and said he could not picture Mrs Clinton as commander in chief.
He saluted veterans, saying they were "so much more brave than me. I'm brave in other ways. I'm financially brave, big deal!".
Mr Trump's path to victory remains narrow. He must win Florida to win the White House - no easy feat. Still, his campaign has been buoyed by tightening polls there and in other key battlegrounds, as well as by signs that African-American turnout for Mrs Clinton may be lagging.
Mrs Clinton enlisted Mr Obama's help, urging those voters to the polls and lighting a fire under other Democrats, particularly young people, who share some of the wariness about her.
Speaking to students at Florida International University in Miami, Mr Obama told voters now was the time to get serious about the choice.
"This isn't a joke. This isn't Survivor. This isn't The Bachelorette," he said, taunting former reality-TV star Mr Trump. "This counts."
Relishing one of his last turns on the campaign stage as president, Mr Obama repeatedly returned to his new campaign catchphrase capturing his disbelief in the unpredictable race to replace him.
"C'mon, man," he said, to cheers.
Mr Obama has been trying to bait the Republican into veering off message - counting on Mr Trump not to have the discipline or the ground game to capitalize on a late surge.
But the famously unconventional Mr Trump has been hewing closer to convention, running some upbeat ads, bringing out his wife for a rare campaign appearance and even talking publicly about trying not to get distracted.
"We don't want to blow it on November 8," he said in Jacksonville.
Mrs Clinton's weekend schedule underscored the Democrats' fresh anxiety in the final stretch. She is due to campaign in Detroit on Friday, where a large turnout of black voters has long been crucial to success, following up on a last-minute meeting by her husband, former president Bill Clinton, with black ministers on Wednesday night.
Mrs Clinton and Mr Obama, along with their spouses, will headline a final pre-election rally in Philadelphia next Monday evening.
Mr Trump has had far fewer allies carrying his message. Senator Ted Cruz, his party primary foe, campaigned with vice presidential candidate Mike Pence outside Des Moines, Iowa, on Thursday, but he never mentioned Mr Trump by name in a 14-minute speech.
Mr Trump's wife Melania made her first appearance on the trail since the Republican convention in July.
At a get-out-the-vote rally in the Philadelphia suburbs, the former model tried to counter the Clinton campaign's pounding attacks on her husband as setting a poor example for children.
She told the group that if she became first lady she would focus on combating online bullying and working against a culture that has "gotten too mean and too rough", she said.
Mrs Trump made no reference to her husband's regular name-calling on social media. On Twitter he has called Mrs Clinton "crooked", ''pathetic", ''liar", ''a fraud" and "very dumb". He has also called Mr Cruz a "true lowlife pol" and a "complete and total liar".