With Clinton, Obama to campaign for his own legacy.

President Barack Obama makes his campaign trail debut with Hillary Clinton Tuesday, his own legacy at stake as he works to elect a Democratic successor.

Appearing onstage with Clinton in Charlotte after lending her a ride from Washington on Air Force One, Obama hopes to confer his relative popularity on a candidate still struggling to gain voters' trust. He'll tout the four years she served as his top diplomat as evidence of tough-nosed grit, and acknowledge that he himself is a Clinton convert after their nasty 2008 primary campaign.

Clinton's campaign aides expect Obama to tell the story of his rival-to-friend relationship with Clinton on Tuesday in North Carolina, offering Americans a validating voice on the former secretary of state's character, fitness and qualifications.

He's also likely to point to his own successes as president -- a record that very much depends his Oval Office replacement to maintain.

"More than anything else he can provide a testimonial for Hillary Clinton, having been her opponent at one point and then working closely with her in her job as secretary of state. And he can describe the demands of the presidency in a way that underscore the seriousness of the job," said David Axelrod, Obama's former senior adviser who now serves as a CNN contributor.

Polls suggest more Democrats trust the President than the candidate herself, and Tuesday's campaign comes amid refreshed scrutiny of Clinton's trustworthiness. Obama will issue his first in-person call for Clinton's election just as his administration completes its investigation into her email practices. The probe brought her to FBI headquarters for an interview Saturday.

The awkward timing is unfortunate for Democrats, who believe Obama can rouse voters not yet clamoring for Clinton. Even as the White House vows utter detachment from the FBI investigation, the question of political interference looms as large as ever.

Former President Bill Clinton's tarmac conversation with Obama's attorney general, Loretta Lynch, only made matters worse.

But any question of waiting until after the Justice Department concludes its work was cast aside as Obama grows increasingly vocal in his denouncement of Donald Trump, and ever more eager to ensure Clinton is elected commander-in-chief.

"The President obviously has had an opportunity to evaluate Secretary Clinton both when they were competing against one another on the campaign trail, but also when she was serving this country as the secretary of state under President Obama. And over the years, the President has developed a deep appreciation for her toughness under fire and her commitment to a set of values that the President shares," White House Press Secretary Josh Earnest said, predicting Obama would refer to those qualities at his campaign stop in Charlotte.

Obama's push for Clinton comes after months of waiting. Like most Democrats, Obama expected his party's primary to conclude far sooner than it did. A postponement after the Orlando terrorist shooting only extended the delay for Obama, who aides say is revving to appear on a campaign stage.

Originally, Obama and Clinton were to appear in Wisconsin, a state whose Democratic primary Sen. Bernie Sanders won handily. But as Sanders continues hinting that he'll soon support Clinton, the campaign opted instead for a stop in North Carolina, which Obama lost narrowly in 2012. The pair will campaign only blocks from the site of that year's Democratic National Convention.

Clinton's top aides believe North Carolina is the biggest must-win for Trump -- and their best chance to flip a state that Mitt Romney won in 2012. Clinton first deployed general election staff to North Carolina in late April and their first ads in the state began running in June.

Underscoring the importance both sides are placing on North Carolina, Trump also campaigns in the state Tuesday, appearing after Clinton during an evening event in Raleigh.

The Clinton campaign and the White House believe Obama can help galvanize the state's large African-American population to vote in November. Defeating Trump will require turning out the coalition of young people, suburban women, and minorities that helped Obama win two presidential elections.

"He's a force multiplier for her," Axelrod said. "When you think about, Donald Trump is really the star of his show, and the the supporting cast. She will have people out there and the president, chief among them, who can really bring the case."

Biden stumps for Clinton in his hometown of Scranton, Pennsylvania, later this week.

For the President, a Trump presidency has become a nightmare scenario that has the potential to undo much of the work he's focused on over the past seven years. As recently as last week, Obama was issuing executive orders in the hopes of institutionalizing the priorities of his administration.

In what's becoming a regular occurrence, Obama used a foreign press conference (in this case, in Canada) to denounce Trump as the antithesis of populism. It wasn't the first time Obama ripped into Trump abroad; less than a month after he announced his candidacy, Obama was shaming Trump for his criticism of Sen. John McCain during a news conference in Ethiopia.

That was perhaps an early sign that Obama wasn't going to let the campaign to replace him proceed without airing his sharp opinions about the Republicans in the race.

With newfound popularity in polls, Obama is expected to use his record as a campaigning point with Clinton, who overwhelmingly shares his policy positions on domestic and foreign affairs.

Their differences -- including on trade and Syria -- aren't expected to be front and center when they take the stage together in Charlotte Tuesday afternoon.

"I don't think the President is going to make the case that Secretary Clinton and he agree on every single issue, but I do think he'll make a pretty persuasive case about how they have spent their careers fighting for the same values and the same priorities," Earnest said.