President Obama formally endorsed Hillary Clinton to succeed him in the White House Thursday, saying she has the "courage" for the job and vowing to hit the campaign trail for her soon -- in a video message posted just moments after meeting with her primary rival Bernie Sanders. 

"I know how hard this job can be. That’s why I know Hillary will be so good at it," the president said, in the video posted on Clinton's campaign site. "In fact, I don’t think there’s ever been someone so qualified to hold this office." 

The president made clear he would no longer stand on the sidelines, even as Vermont Sen. Sanders vows to stick out the race at least through the final primary in Washington, D.C., next Tuesday. 

The Clinton campaign separately announced that she and Obama would campaign together June 15 in Green Bay. Clinton tweeted that she's "fired up." 

Presumptive GOP nominee Donald Trump immediately fired back. 

To which the Clinton campaign tweeted: "Delete your account."

Meanwhile, Vice President Joe Biden voiced his support of Hillary Thursday evening at the American Constitution Society's national convention.

 

"Anybody who thinks that whoever the next president is --  and God willing, in my view, it will be Secretary Clinton."

The White House, meanwhile, said Obama recorded the video on Tuesday, the day Clinton effectively wrapped up the nomination. 

The video was released shortly after Obama met in the Oval Office with Sanders. 

Sanders afterward struck a conciliatory tone Thursday, saying he plans to meet soon with Clinton to discuss how they can “work together to defeat Donald Trump.”

The Vermont senator said he still plans to compete in next Tuesday’s Washington, D.C., primary, the final contest on the calendar. And he said he plans to take his message “to the Democratic National Convention” in July.

He did not, however, say specifically whether he would still be an active candidate by then, taking no questions from the press before heading over to a meeting with Senate Minority Leader Harry Reid.

The meeting with Obama was private. They met for over an hour, and Fox News is told no staff or aides were present.

But his tone, compared with his defiant speech early Wednesday after Clinton clinched the Democratic nomination, appeared to soften.  

While offering no endorsement himself, Sanders said he spoke with Clinton and congratulated her “on her very strong campaign.”

And Sanders thanked Obama for his “impartiality” throughout the process. He said he and Vice President Biden lived up to their pledge not to put their “thumb on the scales.” 

White House spokesman Josh Earnest later said Sanders has the right to make campaign decisions on his own timeline. Another former primary candidate, ex-Maryland Gov. Martin O'Malley, did endorse Clinton, saying "it is time now to unite our party."

Clinton and Obama, along with other party leaders, are eager to bring Sanders – and his supporters – into the fold.

The president's endorsement reflects their desire to unify as the general election battle between Clinton and presumptive rival Trump intensifies.

Sanders acknowledged a common political enemy, railing against Trump in his brief remarks to reporters Thursday afternoon and saying he’ll do everything in his power to prevent Trump’s election.

As for what he wants, Sanders said he’ll continue to fight what he called the “drift” toward an oligarchic society. He lamented childhood poverty rates, crushing college debt, crumbling infrastructure and other woes and said these are the issues he’ll bring to the Philadelphia convention.

Whether that means a fight to overhaul the party platform – or a last-ditch bid to somehow deny Clinton the nomination – remains to be seen.

One demand Sanders was thought to be considering – as part of a party-unity deal -- is the removal of Democratic boss Debbie Wasserman Schultz. Sanders and the DNC chairwoman have been at odds for months, with Sanders’ team long accusing her of helping now-presumptive nominee Clinton.

Whether Sanders sought – and the president would even consider – a Schultz sacrifice is unclear.

“I don’t see how she makes it through the convention,” one Democratic lawmaker told Fox News. “The key to Hillary winning is getting Sanders supporters on board.”

Speculation over Wasserman Schultz’ position has swirled for months, however, and so far she has retained the public support of the White House. Obama also endorsed her earlier this year in her House primary battle.

Asked Wednesday about the possibility of Sanders seeking her removal, Wasserman Schultz said she’s not worried about her job. 

“I'm going to be remaining as the chair of the Democratic National Committee as President Obama has asked me to do until January 21, 2017, and I appreciate the president’s support,” she said.