CHARLOTTE, N.C. — Eight years after Hillary Clinton helped unite Democrats behind Barack Obama’s presidential campaign, he’s returning the favor.

Obama and Clinton are making their first joint appearance of the 2016 campaign Tuesday in North Carolina, hours after FBI Director James Comey announced he was not recommending charges be brought against Clinton for her controversial email practices at the State Department. Still, Comey’s scathing criticism of Clinton — he called her “extremely careless” in her handling of classified information — ensures the matter will continue to hang over her campaign.

Yet Clinton and Obama were all smiles as they stepped off Air Force One after a quick flight from Washington, pausing side-by-side to wave for cameras. Then they walked together to greet supporters on the concrete before leaving in a motorcade.

The timing of the trip pulls the president into a controversy he has at times tried to keep at arm’s length, and the White House said he wouldn’t address the investigation during his speech at the rally. His appearance with Clinton is a potent reminder that it was his political appointee who declined to pursue criminal charges against his preferred successor.

Presumptive Republican nominee Donald Trump, who was making his own campaign stop in North Carolina later Tuesday, tweeted that Comey’s decision was evidence of a “rigged” system.

Democrats hope Obama’s presence on the campaign trail can alleviate voters’ questions about Clinton’s honesty and trustworthiness, some of which stem from the email investigation. The president is expected to outline his own evolution from a Clinton skeptic to one of her biggest boosters.

“I think that he can be very helpful, particularly with Democratic voters and some independent voters who have doubts,” said David Axelrod, the chief architect of Obama’s 2008 race for the Democratic nomination against Clinton. “He can do that by sharing his own experience. They were rivals, they had their differences; that gives him some additional standing.”

The Clinton campaign is also hoping Obama’s presence at her side serves as a reminder of other aspects of her State Department tenure. For four years, Obama trusted her to circle the globe representing his foreign policy. She sat at his side in the Situation Room. She was the good soldier, putting aside her political ego to join the administration of the man who defeated her. During her tenure at the State Department she was viewed favorably by most Americans.

Clinton’s Republican presidential rival objected to the travel plan. “Why is President Obama allowed to use Air Force One on the campaign trail with Crooked Hillary?” Trump tweeted. “Who pays?”

Presidents make all their airplane flights on Air Force One, no matter the purpose of the trip. Political committees are required to contribute to the cost of a president’s campaign-related travel, though a portion of such costs is borne by taxpayers, too.

“As is the standard practice, the campaign will cover its portion of the costs,” Clinton spokesman Nick Merrill said.

Obama makes his first campaign appearance with Clinton during a wave of popularity unlike anything he’s experienced since his first term. Clinton aides say they’re confident they could deploy him in any battleground state, though they believe he’ll be particularly effective in rallying young people, as well as black and Hispanic voters, and will be instrumental in voter registration efforts.

In a series of remarks in recent weeks, the president has proven himself to be one of the Democrats’ most effective critics of Trump. From his perch at the White House and on the world stage, Obama has regularly found ways to blast Trump’s message and mock his style.

Still, Obama won’t spend the next four months as the “Trump-troller in chief,” as one official put it. Obama plans to take a largely positive message on the road as his campaigning picks up later this summer. That’s in part because he’s campaigning for the continuation of his agenda — as well as Clinton’s. On health care, immigration, financial reform and the environment, Clinton is largely promising a continuation or acceleration of Obama’s policies.

Obama and Clinton originally planned to make their first campaign appearance together in Wisconsin, a Democratic-leaning state where Clinton struggled in her primary fight with Bernie Sanders. Campaign aides viewed the rally as a way to forge Democratic unity after the bruising primary and consolidate the party’s voters in a state Clinton needs to carry in November.

But the June 15 rally was postponed due to the mass shooting at an Orlando nightclub. By the time the campaign and White House got around to rescheduling, Clinton aides said the landscape had shifted — they are now far less worried about bringing along Bernie Sanders voters and more interested in using the president to rally voters in one of the most divided general election battlegrounds.

Obama narrowly won North Carolina in the 2008 presidential election, becoming the first Democrat to win the state since 1976. But he was dogged by a sluggish economy and disappointment among some swing voters during his 2012 re-election, and lost to Republican Mitt Romney by 2 percentage points.

UPDATES:  Donald Trump praises Saddam Hussein for killing terrorists ‘so good’ | Analysis: For Hillary Rodham Clinton, character questions to persist |Four reasons why the ‘Dump Trump’ effort will likely fail | FBI says Hillary Rodham Clinton was careless but not criminal | FBI says Hillary Rodham Clinton was careless but not criminal