WASHINGTON — (CNN) Hillary Clinton became the Democratic Party’s presumptive presidential nominee this week — but for her challenger Bernie Sanders, the fight is not quite over.

The Vermont senator declared Tuesday night that he intends to continue his White House campaign and declined to acknowledge that Clinton had secured the necessary delegates to win her party’s nomination. At the tail end of the primary season, Sanders vowed to forge ahead to the District of Columbia’s primary next week, and then on to the Democratic National Convention in Philadelphia.

This decision has Democrats on high alert, as they look to quickly gears and take on the presumptive Republican presidential nominee, Donald Trump.

Thursday has the potential to shed light on the senator’s intentions and state of mind as the general election kicks off in earnest.

Sanders will meet with President Barack Obama in their second White House sitdown this primary season and the fourth time they’ve spoken in the last month. Aides said Obama would work to move Sanders toward an acceptance of Clinton as the nominee.

In their meeting, Obama won’t directly ask Sanders to exit the race, and senior Democrats say it’s unlikely Obama will make any joint appearances with Clinton before next week’s primary, the final nominating contest this year. However, a formal Obama endorsement could come earlier — perhaps as early as Thursday — though not before Obama sits down with Sanders.

While it’s unlikely that Sanders emerges in full support of Clinton, White House officials hope Obama can prod the Vermont senator toward eventually acting as a unifying figure for the Democratic Party.

“My hope is, is that over the next couple of weeks, we’re able to pull things together,” Obama told Jimmy Fallon during a taping of “The Tonight Show” Wednesday. “The main role I’m gonna be playing in this process is — to remind the American people that this is a serious job. You know, this is not reality TV. I’ve seen the decisions that have to be made. And the work that has to be done. And I have a lot of cornfidence that if the American people are reminded of what’s at stake and all the incredible important issues that we gotta get right, that they’re gonna make a good choice. That’s what they usually do.”

Sanders will also meet with Senate Minority Leader Harry Reid — who has publicly said Sanders should “give up” — and has a campaign rally scheduled in Washington in the evening.

Sen. Jeff Merkley of Oregon, who has endorsed Sanders, told CNN on Wednesday that he is confident Sanders is committed to unifying the party and helping to defeat Trump in November.

Continuing his campaign, Merkley said, is Sanders’ way of ensuring that the voices of his supporters are heard.

“If you ask people to shut down a race early and their supporters don’t have a chance to express themselves, it’s much less likely they’re going to come together afterward,” Merkley said. “I think it’s been very valuable to the party and to our nominee to have had the campaigns run their course and have everybody in America be able to participate.”

Since clinching her party’s nomination, Clinton has stuck to a conciliatory tone when it comes to her rival.

In her victory speech in Brooklyn Tuesday night, Clinton congratulated Sanders for an “extraordinary campaign” and sought to reach out to his supporters.

“Let there be no mistake: Sen. Sanders, his campaign, and the vigorous debate that we’ve had about how to raise incomes, reduce inequality, and increase upward mobility, have been very good for the Democratic Party and for America,” Clinton said.

As a part of an overarching strategy to bring Sanders fan into the fold, the Clinton campaign and its surrogates have no plans to call on the senator to get out of the race.

Still, Sanders’ stubborn refusal to drop out of the 2016 race and his sharp criticism of Clinton have irked plenty of Democrats.

Former Rep. Barney Frank, a co-chair of the party’s Rules Committee, has exchanged harsh words with Sanders. The senator asked the Democratic National Committee to remove Frank and Connecticut Gov. Dannel Malloy from their co-chairmen positions, calling them “aggressive attack surrogates for the Clinton campaign.”

In an interview with CNN on Wednesday, Frank said he believes Sanders has “stirred up” anger among his supporters against Clinton. Sanders has every right to stay in the race, Frank said, but he also has a responsibility to bring them around to the party’s nominee.

“I have a profound difference with his approach to how you bring about progressive change,” Frank said. “I would hope that he would spend some of his energy persuading those people that they don’t have to like her but if they believe in the values that his campaign is advancing, they have to help her beat Donald Trump.”

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