Time to get serious, President Barack Obama told voters Thursday, denouncing Republican Donald Trump as a "con artist" and a threat to democracy as the race for the White House opened its do-or-die phase.

"This isn't a joke. This isn't 'Survivor.' This isn't 'The Bachelorette.'" Obama said, taunting the former reality-TV star. "This counts."

Obama tore into Trump as the Republican is closing on Democrat Hillary Clinton with just five days left. Speaking to students in all-important Florida, Obama tried to light a fire under complacent Democrats and frame the stakes. He zig-zagged from mockery to dire warnings to boasting about his own record in office. And he repeatedly returned to his new campaign catchphrase capturing his disbelief in the unpredictable race to replace him.

"C'mon, man," he said, to cheers.

The president's taunts were aimed at firing up the Democratic base and baiting the Republican into veering off message. Democrats are counting on Trump, who is also campaigning in Florida on Thursday, not to have the discipline to capitalize on a late surge.

Trump so far hasn't bit. The unconventional Republican candidate is trying to hew closer to convention, running some upbeat ads, bringing out his wife for a rare campaign appearance and trying, publicly, not to get distracted.

"'Stay on point, Donald, stay on point,'" Trump teasingly quoted his staff as saying, as he campaigned Wednesday in Florida. "No sidetracks, Donald. Nice and easy. Nice and easy.'"

On Thursday, he needled Obama, as he looked at the president's plane at Miami International Airport.

Trump tweeted:

Looking at Air Force One @ MIA. Why is he campaigning instead of creating jobs & fixing Obamacare? Get back to work for the American people! — Donald J. Trump (@realDonaldTrump) November 3, 2016

Trump's wife, Melania Trump, was to campaign in a suburb of Philadelphia on Thursday, her first turn on the trail since the Republican convention in July. The former model is trying to counter the Clinton campaign's pounding attacks on her husband as anti-woman, a strategy Democrats see as the best hope for rattling him and driving female voters away from him.

In excerpts of Melania Trump's prepared remarks, distributed by the campaign, she said, "I come here today to talk about my husband, Donald, and his deep love and respect for this country and all of its people."

Clinton stuck with her sharp-edged closing argument as polls showed her once-hefty lead noticeably trimmed in recent days. News that the FBI is reviewing her close aide's emails appears to have revived questions about her trustworthiness just as many late-deciding voters were making up their minds.

Clinton's campaign has responded by trying to keep the spotlight on Trump, and specifically his history of vulgar and disparaging statements about women, minorities and people with disabilities.

The campaign said it would bring Clinton and Obama together, along with their spouses, for a final pre-election rally in Philadelphia on Monday evening.

Pennsylvania does not offer early voting, leaving Election Day turnout as key. But Florida looked to be the linchpin to Trump's chances.

He can't win the election without carrying Florida, a fact that highlights how narrow his path is. He campaigned in three Florida cities Wednesday — Miami, Orlando and Pensacola — and will follow up with a stop in Jacksonville on Thursday.

"We don't want to blow this," he told rowdy supporters in Miami. "We gotta win. We gotta win big."

Trump's confidence aside, Clinton still has more paths to victory — and was looking for even more. She made a late stop Wednesday in reliably Republican Arizona, where Trump's unpopularity among Hispanic voters has given Democrats hope.

"This state is in play for the first time in years," Clinton exclaimed during a nighttime rally on the campus of Arizona State University. She was greeted by a boisterous crowd of 15,000, one of her largest of the campaign.

But Clinton's hopes for a landslide appear to be fading. Polls show Trump closing in on her in battleground states, including some where Clinton has led for weeks.

The campaign and its allies were spending additional money in Michigan and Colorado, states long considered solidly in Clinton's column.

Early voting numbers in some states suggest that her challenge stems, at least in part, from underwhelming support from African-American voters.

Early voting in North Carolina shows a 5 percentage point drop in ballots from black voters from 2012.

Former President Bill Clinton made an unannounced appearance in Detroit Wednesday night to meet privately with black ministers, the city's mayor and other local leaders. Hillary Clinton planned to travel to the Detroit area on Friday.

The National Republican Senatorial Committee, meanwhile, said it saw new hope for its candidate in Wisconsin, a state that favors Democrats in presidential election years. The committee will spend close to $1 million in several media markets, including Milwaukee and Green Bay, on behalf of the GOP incumbent, Ron Johnson, long considered one of the most vulnerable senators.

Private and public polls show a single-digit difference between Johnson and Democratic rival Russ Feingold.

Republicans are battling ferociously to protect their 54-46 majority in the Senate ahead of Tuesday's election. They are on defense around the country, but a number of close races are essentially toss-ups in states such as Pennsylvania and New Hampshire.