Barack Obama spent several hours last Friday in the family dining room of the White House, visiting his former vice president, Joe Biden. The mood was cheerful as the pair exchanged jokes, and the meeting served as a small reunion of sorts for the two presidents' respective staff – many of whom have known each other going back to the Obama White House. Still, the occasion was hardly just two old friends catching up. Obama has made clear to associates in recent months that he believes Biden's intensifying re-match with Donald Trump in November will be incredibly close, and that the 2024 election marks an "all-hands-on-deck" moment, people familiar with his thinking told CNN. To that end, his return to 1600 Pennsylvania Avenue last week was largely a working visit. Biden and Obama, along with former House Speaker Nancy Pelosi, participated in an organizing call in the White House residence heralding the 14th anniversary of the Affordable Care Act. "We have the chance to do even more, but that only happens if we send Joe and Kamala back to the White House in November," Obama said in the video. "So, we've got to keep working." Off camera, Obama told Biden that he thought the president's State of the Union remarks earlier this month had been effective and were breaking through, according to people familiar with their conversation. Obama also emphasized to Biden how much he believes health care will be a politically potent and important issue in the upcoming election. The campaign also recorded other content featuring the two presidents, sources said, that they plan to roll out in the coming weeks. Obama and Biden speak with regularity, sources said, and the former president remains in direct contact with some top White House officials, including Biden's chief of staff, Jeff Zients, who worked in the Obama administration. The former president has lent an occasional hand to Biden since the current president's reelection announcement last year, particularly through public fundraising appeals and in quiet conversations in hopes of allaying concern from some Democrats about Biden seeking a second term. His engagement with the Biden campaign is expected to intensify as the general election kicks into higher gear, and aides said he has already agreed to several campaign appearances before November as he works to help rebuild Biden's winning coalition from 2020. Obama's biggest embrace of Biden's reelection effort comes Thursday at a star-studded Manhattan fundraiser featuring Biden, Obama and former President Bill Clinton. The three presidents will sit for a rare conversation, moderated by Stephen Colbert. It will hardly be a routine meeting of the Presidents Club, and when Clinton and Obama take the stage at Radio City Music Hall, their appearance will underscore the extraordinary moment in American history as a sitting president is locked in a bitter fight to keep his predecessor from returning to the White House. "No one can speak to disillusioned Democrats better than President Obama," a senior strategist who has worked closely with Obama and Biden told CNN, speaking on condition of anonymity to be candid about the campaign. "But there are limits to what Obama can do. The burden to win this race is still on President Biden." Attending the sold-out, high-dollar event Thursday night will be numerous celebrities and artists like Queen Latifah, Lizzo, Cynthia Erivo, Mindy Kaling, Ben Platt and Lea Michele, according to the campaign. The evening will be overseen by high-profile producers Jordan Roth and Alex Timbers, and tickets will range from $225 to $500,000. Capitalizing the rare joint appearance of Biden and two of his predecessors, the campaign is offering some of the high-dollar guests the opportunity to get their photographs taken with all three presidents by famed photographer Annie Leibovitz. As president, Biden has also been in frequent touch with Clinton, sources familiar say. Steve Ricchetti, a top Biden adviser who also worked in the Clinton White House, is also in regular touch with his former boss. Advice and consultation related to the 2024 election have been a part of all of those conversations, those people said. Obama's appeal and popularity as one of the best-known national Democrats has been undeniable. The campaign's grassroots fundraising efforts featuring the former president have raised over $15 million so far this cycle, with a "Meet the Presidents" contest featuring Biden and Obama alone hauling in some $3 million, according to the campaign. For the next seven months, a specific area of focus for Obama will be making fundraising appeals and helping to motivate young Americans, particularly Black and Latino voters, who are seen by campaign advisers as a weak spot for Biden's candidacy. Obama has no plans to hit the stump aggressively until the fall, when early voting begins, following a pattern he has adopted since leaving office. Saving the former president until the end of the race — at the time when voters are paying the most attention — is how Obama and his advisers believe he can be the most effective. No firm travel plans have yet been made, aides said, but the former president is likely to visit college campuses in the fall as well as major cities in battleground states. Obama has not been shy in voicing his concern about Israel's war in Gaza, which has become one of Biden's biggest challenges — both in foreign policy and in domestic politics. That, along with reproductive rights, will be the chief focus of Obama's pitch to voters. Jim Messina, Obama's 2012 campaign manager who has been serving as a close adviser to the Biden reelection campaign, told CNN that his former boss plans to do whatever he can to help Biden secure a second term at the White House. That mission, Messina said, has only been made significantly more urgent by Trump's emergence as the presumptive Republican nominee. "President Obama once said to me that every president is a reflection of the previous president, and he's right," Messina said. "Trump was the complete opposite of Obama, and Biden is the complete opposite of Trump. Being the president of the United States means you're part of a small club; there is no other group of people whose red flags about the direct threat of Donald Trump should be taken more seriously." Obama has been unambiguous about his willingness to be of service to his former vice president's reelection efforts, one senior Biden adviser told CNN. "He has been generous with his time, and he has made it very clear that he is all in on this campaign," the adviser said. — CNN