As President Barack Obama started a months-long campaign for Hillary Clinton, the two made their first appearance together Tuesday in a state Obama was able to wrest from Republicans at least once: North Carolina.

They also hope to carry some presidential charm, as well as warnings about Donald Trump’s capacity to serve as commander-in-chief, to swing states such as Florida, Virginia, Ohio and Colorado that will settle the contest.

For Clinton, it’s an opportunity to bask in the modest popularity of a president whose public approval ratings hover above 50 percent — higher than hers — and rally young and minority voters key to Obama’s twin electoral victories.

For Trump, it’s an invitation to portray a Clinton presidency as the third term of an administration he accuses of allowing American jobs to flow overseas and illegal immigrants — including potential terrorist threats — to flourish unchecked.

“Hill-ar-y, Hill-ar-y,” Obama chanted, shirtsleeves rolled, “all fired up” in full-bore campaign mode at Charlotte’s Convention Center. Averting mention of Trump by name, the president repeatedly ridiculed the Republican’s penchant for social media as he painted contrasts in leadership.

“Everybody can tweet, but nobody actually knows what it takes to do the job until you sit behind the desk,” Obama told the crowd. “Hillary Clinton has been tested… There has never been anybody, any man or woman, more qualified for this office than Hillary Clinton… and that’s the truth. The bottom line is, I know Hillary Clinton can do the job… I have had a front-row seat to her judgment.”

Both Obama and Clinton mentioned their moment in the White House Situation Room when he made the call to seize 9/11 mastermind Osama bin Laden in hiding. “This, my friends, is a president who knows how to keep us safe and strong,” Clinton said. “Compare that to Donald Trump. Can you imagine him sitting in the Oval Office the next time America faces another crisis?… Donald Trump is simply unqualified and temperamentally unfit to serve as president of the United States.”

“We have a president who’s out campaigning for crooked Hillary Clinton, and he should be at home working on ISIS, where the crisis is getting worse and worse,” Trump said later, campaigning in Raleigh, N.C. “We’ve got a person in the White House who’s having a lot of fun — it’s like a carnival act…. And we’ve got Hillary Clinton, who’s weak, who’s ineffective. She’ll never be able to do the job. Her judgment is horrible. Look at her judgment on email.”

Two veterans of recent Democratic and Republican campaigns agree on the potential influence of a popular president, while some experts question the wisdom of a candidate as experienced as Clinton calling in reinforcements.

“The last two presidents who were this popular at this point in their presidencies were Bill Clinton and Ronald Reagan, who were followed in both cases by candidates from their party who won the popular vote — Al Gore’s mistake was that he didn’t use Clinton more,” says Steve McMahon, a Democratic consultant who campaigned for Howard Dean. “You are part of Barack Obama’s presidency whether you want to be or not, so you might as well embrace it, be who you are.”

Kevin Madden, a Republican consultant who has campaigned for Mitt Romney and George W. Bush, sees the Obama-Clinton alliance two ways.

“The downside is, at a time when voters are certainly wary about a third term or want to see the status quo shaken up… Hillary Clinton has a hard time with that already. When you have the incumbent campaigning for you, that puts the credentials of offering something new into question,” Madden says. Yet “what really drives the fundamentals of the campaign in this environment is the approval rating of the incumbent in office. The greatest gift President Obama could give Hillary Clinton on Election Day is being above 50.”

Obama’s job approval has generally held above 50 percent in Gallup polls since March — 56 in the latest ABC/WashingtonPost survey, his highest in five years.

He will concentrate efforts for Clinton where he stands to make the most difference. North Carolina is one of only two states that Obama narrowly won in 2008 and lost in 2012 — the other, Indiana. It’s also one of two Southern states that went Democratic in 2008 for the first time since the 1960s — the other, Virginia — and one of eight battleground states where Clinton is airing TV ads.

Polls show Clinton and Trump virtually tied in North Carolina, scene of disputes over a state law restricting public bathrooms to one’s gender at birth. Obama and Clinton, courting LGBT voters, were stumping in Charlotte, home of an anti-discriminatory ordinance prompting the state law as a reaction.

Trump, countering Clinton with an appearance in Raleigh, N.C., Tuesday, maintains the “people of North Carolina want strength, protection and jobs, and President Obama and Hillary Clinton have let them down for many years.”

While sidelined furniture and textile workers hit hard by the Great Recession are open to Trump’s anti-free trade talk, the state also is home to burgeoning banking, high-tech and pharmaceutical ventures keen for exports. In a state with 90-percent white voters in 1992, just 70 percent are today, and the minority voters are mainly Democrats.

“What’s happened here that keeps this state purple and a swing state and gives Clinton buoyancy here is this biracial coalition,” says Ferrel Guillory, director of the Program on Public Life at the University of North Carolina at Chapel Hill. “The campaign is going to come down to voter mobilization….That’s why Obama helps her. He’s got the juice when it comes to mobilization.”

This is true nationally, as well. “What Hillary Clinton needs most is a unified convention, bringing together the Obama coalition of younger people and minority voters,” Madden says. “Nobody does that better than President Obama…The data that’s driving these decisions is the need to consolidate the Democratic base.”

Yet the sword of this modern-day “Team of Rivals” could cut two ways.

“For those who want change, and there’s a big desire for change, tying yourself to the incumbent undermines that,” says John Geer, a political scientist at Vanderbilt University. “At the same time, the economy is doing fairly well, his numbers are above 50 percent, and that’s something you want to tie your wagon to.”

“My advice is always unequivocally, stay in your own lane, run your race,” says Republican pollster David Hill. “Clinton’s going to have some net loss, or some net gain, from this. She probably doesn’t know the calculus of it, so why do it?”

Like Clinton, Obama has hit Trump hard. “We are in serious times and this is a really serious job,” Obama said as Trump was securing his nomination. “This is not entertainment, this is not a reality show.”

“It’s pretty hard to argue that somebody who almost three-quarters of the country thinks is unqualified to be president and has a negative opinion about is tapping into the zeitgeist of the country,” Obama said in an interview with NPR.

At a recent conference with Canadian and Mexican leaders in Ottawa, without identifying Trump by name, Obama suggested that his campaign rhetoric is “not the measure of populism. That’s nativism or xenophobia… or worse.”

For his part, Trump is attempting to hang some of the crises of Obama’s administration on Clinton, former secretary of state, as well as a now-finished FBI investigation of her private email server as secretary.

After the FBI interviewed her Saturday, Trump tweeted reports that “no charges will be brought against Crooked Hillary Clinton. Like I said, the system is totally rigged!’’ And as FBI Director James Comey formally announced Tuesday before Obama and Clinton headed to Charlotte that there will be no charges, Trump tweeted again: “Wow! #RiggedSystem’’

He has tweeted: “ISIS exploded on Hillary Clinton’s watch — she’s done nothing about it and never will.” And on the 2012 killing of the U.S. ambassador to Libya and three other Americans: “Benghazi is just another Hillary Clinton failure. It just never seems to work the way it’s supposed to with Clinton.”

Obama and Clinton will always have Osama bin Laden, killed on their watch. And the White House says CIA and military counterterrorism strikes have killed as many as 2,581 “combatants” through 2015 — “There isn’t a president who’s taken more terrorists off the field than me,” Obama told Fox News in April.

Over the weekend, as Trump faced criticism for a tweet attacking Clinton with a meme originating from a white-supremacist account, Clinton tweeted her own plans: “Looking forward to hitting the campaign trail together, @POTUS.”

Clinton also will campaign with Vice President Joe Biden at his home town of Scranton, Pa., on Friday — Biden’s job approval also running above 50 percent.

At the same time, a fray like this year’s race can take a toll on anyone’s popularity.

“One of the reasons (Obama) is above 50 percent right now is that he looks less political than the other candidates in the race,” Madden says. “Remember, Hillary Clinton was popular as secretary of state…The problem for President Obama is getting into the arena to campaign for Clinton and losing that favorable rating.”

Editor’s note: this post was updated to include comments from the Clinton campaign rally and reaction from Donald Trump.