JACKSONVILLE, Fla. — Donald Trump warned Thursday that a cloud of investigation would follow Hillary Clinton into the White House, evoking the bitter impeachment battle of the 1990s in a closing campaign argument meant to bring wayward Republicans home.

Clinton and her allies, led by President Barack Obama, told voters to get serious about the dangers of Trump.

As polls show Trump closing in on 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.

Clinton’s shrunken lead has given Trump’s campaign a glimmer of hope, one he’s trying to broaden into a breakthrough before time runs out.

That means zeroing in on questions of 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 behavior but equally repelled by the possible return of the Clintons.

“Here we go again with the Clintons — you remember the impeachment and the problems,” Trump said Thursday at a rally in Jacksonville. “That’s not what we need in our country, folks. We need someone who is ready to go to work.”

Clinton and allies, meanwhile, are seeking to keep the spotlight on 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,” Clinton said, singling out 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,” Clinton said.

“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.

Clinton campaigned later Thursday with former primary opponent Sen. Bernie Sanders and pop star Pharrell Williams in Raleigh, where she warned that Trump’s election risked “normalizing discrimination.”

Also in battleground North Carolina, Trump delivered a defense-related speech at a nighttime rally and said he can’t picture Clinton as commander in chief. And he saluted veterans, saying, they are “so much more brave than me. I’m brave in other ways. I’m financially brave, big deal!”

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 Clinton may be lagging.

Clinton enlisted 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 Clinton. Speaking to students at Florida International University in Miami, 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 the former reality-TV star. “This counts.”

Relishing one of his last turns on the campaign stage as president, 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.

Obama has been trying to bait the Republican into veering off message — counting on Trump not to have the discipline or the ground game to capitalize on a late surge.

But the famously unconventional 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 Nov. 8,” Trump said Thursday at the rally in Jacksonville, his fourth in Florida in two days.

Clinton’s weekend schedule underscored the Democrats’ fresh anxiety in the final stretch. She is due to campaign Friday in Detroit, where a large turnout of black voters has long been crucial to success, following up on a last-minute meeting by former President Bill Clinton with black ministers on Wednesday night.

Clinton and Obama, along with their spouses, will headline a final pre-election rally in Philadelphia next Monday evening.

Trump has had far fewer allies carrying his message. Sen. Ted Cruz, his GOP primary foe, did campaign with vice presidential candidate Mike Pence outside Des Moines, Iowa, on Thursday, but he never mentioned Trump by name in a 14-minute speech.

Trump’s wife, Melania Trump, 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 becomes first lady she will focus on combatting online bullying and working against a culture that has “gotten too mean and too rough,” she said.

Melania made no reference to her husband’s regular name-calling on social media. On Twitter, Donald Trump has called Clinton “crooked,” ”pathetic,” ”liar,” ”a fraud” and “very dumb.” He has called Cruz a “true lowlife pol” and a “complete and total liar.”

Trump’s daughter Ivanka was campaigning in New Hampshire.

Associated Press writers Darlene Superville in Miami, Julie Pace in Raleigh, North Carolina and Errin Haines Whack in Berwyn, Pennsylvania contributed to this report.