The epicenter of the presidential campaign shifted to New York on Thursday, as the incumbent president and three of his predecessors descended on the area for dueling events that illustrated the kinds of political clashes that could come to define the general election.

For Democrats, it was a high-profile fund-raiser for President Biden in Manhattan. On Long Island, former President Donald J. Trump attended a wake for a New York City officer who was killed during a traffic stop on Monday. Together, the day’s events made for an unusual moment in a general election campaign that has so far been largely defined by appearances in courtrooms and at small, invitation-only events. In recent weeks, Mr. Trump has spent far more time battling in court than in battleground states.

Mr. Biden, along with Barack Obama and Bill Clinton, arrived for a joint fund-raiser at Radio City Music Hall that campaign aides said raised $25 million. The eye-popping number set a record for a single political event, according to aides, and offered a star-studded show of Democratic unity as the president heads into a difficult re-election campaign.

Mr. Trump, the presumptive Republican nominee, made his own appearance in the area several hours earlier, at a funeral home on Long Island. His campaign used the stop to draw a sharp contrast with Mr. Biden, attacking the Democrats for spending their evening with donors and celebrities.

Mr. Biden, meanwhile, has increased the pace of his events since his State of the Union address early this month. But the fund-raiser, with an expected 5,000 donors, will be one of the largest crowds he has appeared before as president. It will expand an already significant cash advantage, too, raising in one night $5 million more than Mr. Trump reported collecting in February.

“This historic raise is a show of strong enthusiasm for President Biden and Vice President Harris and a testament to the unprecedented fund-raising machine we’ve built,” said a campaign co-chair, Jeffrey Katzenberg.

The day’s events underscored a central dynamic of the race: Mr. Biden is campaigning with the force of the Democratic establishment behind his bid, as Mr. Trump stands largely alone.

While Mr. Trump has been endorsed by many Republicans in Congress, a small but persistent wing of the party has declined to support his third run for the White House. The only living former Republican president has not endorsed his bid, nor has Mike Pence, his former vice president.

Mr. Biden faces a different problem. Nearly all Democratic Party officials, politicians and strategists stand behind his effort. Yet, he has faced sustained opposition from a vocal minority of progressives who have protested the war in Gaza, through protest votes and event disruptions.

On Thursday, a group of several hundred protesters marched through the rain to stand outside the fund-raiser. “Biden, Biden, you’re a liar, we demand a cease-fire,” they chanted.

Inside the hall, the three presidents were scheduled to appear onstage before nearly 5,000 attendees for a conversation moderated by the late-night talk show host Stephen Colbert. A musical program, hosted by the actress Mindy Kaling, will feature a series of celebrity endorsers including Queen Latifah, Lizzo, Ben Platt, Cynthia Erivo and Lea Michele.

Only a small group of press traveling with the White House was allowed in the event and video footage by the news media was prohibited. Before the fund-raiser, the three presidents participated in a joint interview on “Smartless,” a podcast hosted by the actors Jason Bateman, Will Arnett and Sean Hayes.

Mr. Trump’s appearance struck a decidedly different tone. The former president spent about 30 minutes inside a funeral home in suburban Massapequa on Long Island, visiting with the widow and 1-year-old son of Officer Jonathan Diller. Mr. Diller was fatally shot during a traffic stop on Monday.

While not an official campaign event, Mr. Trump took the opportunity to press his tough-on-crime message. Mr. Trump, who is facing four criminal cases, including one in Manhattan that is going to trial in less than three weeks, stood in front of more than a dozen police officers and proclaimed the need for the country to “get back to law and order.”

His campaign pushed a different message, drawing a sharp contrast between Mr. Trump’s visit and the other political event happening in the region.

“President Trump will be honoring the legacy of Officer Diller,” Steven Cheung, a campaign spokesman, said on social media.

Mayor Eric Adams of New York, who attended the wake after Mr. Trump, told reporters that Mr. Biden had called him to offer condolences that Mr. Adams said he would relay to the family. Karine Jean-Pierre, the White House press secretary, said Mr. Biden has supported law enforcement officers throughout his entire career.

“Violent crime surged under the previous administration,” she said, speaking aboard Air Force One, as the president traveled to New York City. “The Biden-Harris administration have done the polar opposite, taking decisive action from the very beginning to fund the police and achieving a historic reduction in crime.”

Michael Gold and Julian Roberts-Grmela contributed reporting.