Two days after Hillary Clinton secured enough delegates to be the presumptive nominee of the Democratic Party, President Obama endorsed Clinton Thursday in a video. The two will campaign together next week in Wisconsin.
"I want to congratulate Hillary Clinton on making history," Obama says in a video. "I know how hard this job can be. That's why I know Hillary will be so good at it. I don't think there's ever been someone so qualified to hold this office."
Shortly after the endorsement, Clinton told NPR, "Well, I'm thrilled that the president has endorsed me. We started off as fierce competitors. We've ended up as true friends."
The endorsement comes the same day Obama met at the White House with Vermont Sen. Bernie Sanders, Clinton's chief rival for the Democratic nomination. It also comes as Democratic leaders are seeking to unify ahead of the general election.
The two talked for about an hour in the Oval Office. Before the meeting, Sanders and Obama strolled down the colonnade en route to the Oval smiling for the gathered television cameras.
Afterward, Sanders thanked Obama and Vice President Biden for their impartiality during the primary process, but he did not concede or endorse Clinton. He vowed to fight on to the Washington, D.C., primary, which takes place Tuesday, the last voting of the primary process. (Sanders even declared that he is "strongly in favor of D.C. statehood.")
Sanders said Clinton had run a "strong campaign" and that he looked forward to meeting with her in the near future to see how they can "work together to defeat Donald Trump" and create a government that "doesn't just fight for 1 percent."
Obama will certainly campaign for Clinton this fall. Having a president campaign strongly for his successor is a surprising rarity in American politics. It hasn't happened in at least 100 years.
Bitter rivals to allies: How President Obama evolved on Hillary Clinton
A lot can change in eight years.
Back then, President Obama helped keep Hillary Clinton out of the White House. Now he's endorsing her bid for president.
He's likely to be one of her best campaign weapons.
"I've gotten to know Hillary really well," the president told Glenn Thrush on a Politico podcast, "She is a good, smart, tough person who cares deeply about this country."
That's what he says now.
The two were a lot less chummy in the winter of 2008, when they waged a bitter primary battle. Clinton shamed Obama, telling him to run a campaign consistent with his messages in public.
And Obama said that while he was a community organizer, watching as jobs were shipped overseas, Clinton was a "corporate lawyer sitting on the board at Walmart."
He said he barely found Clinton "likable enough."
As we know, Obama won the nomination. And days later, the two candidates held a secret meeting. They huddled privately at the Washington home of Sen. Dianne Feinstein to bury the hatchet.
"They were able to talk through a lot of the things that had gone on in the primary," recalled Tommy Vietor, one of Obama's original staffers, "and when she gave that speech endorsing him, that was an enormous step forward in terms of bringing the party back together, mending their relationship."
But the staffers from the two campaigns were not so quick to mend fences. Neera Tanden had been Clinton's policy director and after the primary, she went to work for Obama.
"Having been on the campaign side, I can tell you Barack Obama was a lot faster getting past the primary than the vast majority of his campaign," Tanden says.
Indeed, many of Obama's loyalists were stunned when he picked Clinton to be his secretary of state.
"I was absolutely floored. It was a total shock," Obama speechwriter Ben Rhodes told former political adviser David Axelrod in a podcast, "There were some hard, raw feelings in that campaign."
The tension flowed both ways. Rhodes says Clinton staffers would stop talking when he walked into a room. Obama staffers vetoed Clinton's effort to appoint one of her trusted allies, Sidney Blumenthal, to a State Department post.
Clinton's own emails suggest that she had trouble penetrating the insular White House culture at first. But Rhodes says the secretary quickly won him over, once he was assigned to help Clinton through her confirmation hearing.
"She could not have been more warm. She could not have been more gracious," Rhodes said. "Everything people say about working with her is true. She just totally threw herself into the job from the second she accepted it. So that made it much easier to kind of quickly leave that past behind."
Rhodes says another milestone came in the winter of 2009 when the president and the secretary attended the Copenhagen climate summit together. The summit failed to produce much of a climate agreement but it did improve the working climate between Obama and Clinton. They were forced to improvise as they chased down foreign leaders.
"They had to spend the whole day in shuttle diplomacy with the Chinese and the Indians and the Europeans," Rhodes said, "but they were enjoying themselves."
For four years, Clinton served the president as a loyal and hard-working cabinet secretary. Now that she's a candidate, she's chosen to distance herself from the administration on some issues: She recently came out against Obama's Pacific trade deal and she's long been more hawkish than the president towards Syria.
Despite those differences, Tanden says Obama will be a potent campaigner for Clinton. His overall approval rating now tops 50 percent. And he'll play an especially important role in trying to mobilize the young and minority voters who twice helped to elect him.
"Hillary isn't running for the third term of President Obama," Tanden said, "But obviously they share core principles. And I think he would be very comfortable campaigning for her."
Clinton herself has said Obama is a more natural retail politician than she is. And while Obama's not on the ballot, he is itching to help out.
After all, many of his own policies and his legacy depend on keeping a Democrat in the White House.