It’s Donald Trump’s 78th Birthday. He Isn’t Happy About It.

“Donald hates his birthdays,” Ivana Trump once said of her former husband.

He seemed to hate this one, on Friday, especially. He looked genuinely upset earlier this week when his supporters sang an early “Happy Birthday” to him at a rally in Las Vegas. “You know,” he told them, “there’s a certain point at which you don’t want to hear ‘Happy Birthday.’ You just want to pretend the day doesn’t exist.”

No doubt. Now 78, he is trying to convince the country to give him another four years in office, at the end of which he would be the oldest president in American history — a mantle held by the current, 81-year-old occupant of the Oval Office.

On the campaign trail, both men try to downplay their age while making the other appear as creaky and cranky as possible.

The Trump team spent the week blasting out selectively edited videos of Mr. Biden toddling around Europe, looking like Corrado Soprano lost in Newark. “We have a president who has no clue what the hell is going on,” Mr. Trump said at a birthday celebration with supporters in Palm Beach, Fla., on Friday evening.

The Biden campaign hit back with an email on Mr. Trump’s birthday, reminding voters that he had fallen asleep at his own trial, a case that resulted in felony convictions. “He is unhinged, unable to focus and diminishing before our very eyes,” James Singer, a Biden campaign spokesman, said of the former president.

Mr. Trump used to have fun on his birthdays. “Donald was the child who would throw the cake at the birthday parties,” his younger brother Robert once told the journalist Marie Brenner. After he became a mogul, Mr. Trump would throw swinging parties at his casinos in Atlantic City, N.J., like the one at Trump’s Castle in 1988, for his 42nd birthday, when he played videos of Liza Minnelli and Billy Crystal wishing him a happy birthday. (President Ronald Reagan sent a telegram.)

Two years later, Mr. Trump’s birthday party was hosted by Robin Leach, from the TV show “Lifestyles of the Rich and Famous.” Dolly Parton and Elton John sent videos, Andrew Dice Clay performed, and a George H.W. Bush imitator declared that Mr. Trump should one day be president. At Mr. Trump’s 50th birthday celebration, in Trump Tower in New York, Eartha Kitt sang to him, and there was an ice sculpture of Marla Maples, then his wife, in mermaid form.

There were not any mermaids or Catwomen at his 78th. It was held at the Palm Beach County Convention Center near the airport by a group of supporters who call themselves Club 47 USA, a hopeful reference to Trump’s aspiration to become the 47th president. General admission cost $25.

“There’s nowhere else I’d rather be,” Mr. Trump said to hundreds of his supporters who filled the convention center, some pushing and cursing at one another to get a spot nearer the stage, where a tiered cake sat. Images of Mr. Trump playing golf and sitting behind the resolute desk were painted into the icing. (The cake also wore a red MAGA hat.)

The last time he addressed this group, in October, he opened up about the day that he ordered a drone strike on Iran’s top security and intelligence commander, Maj. Gen. Qassim Suleimani.

“Nobody’s heard this story before,” Mr. Trump told them. “But I’d like to tell it to Club 47, because you’ve been so loyal.” He also talked at that event about his disappointment with Prime Minister Benjamin Netanyahu of Israel — even though it was only four days after the Hamas-led Oct. 7 attack on the country. “I’ll never forget that Bibi Netanyahu let us down,” Mr. Trump said then.

His only living sibling, Elizabeth Trump, had turned up for the birthday event Friday. “Where’s Elizabeth?” he asked from the stage. “Right there. My beautiful sister. She’s a great sister. Great one.”

Also, there was Marco Rubio, a vice-presidential contender who had been taking a subtle approach to auditioning for the job. “I’m going to be honest with you,” Mr. Rubio said from the stage. “Sometimes, I think, Why is this guy doing this? He had a great life. He didn’t need to be in politics. There’s only one reason why someone like him would be in politics, with all of these hassles, with all of these things he has to put up with. There’s only one reason — because he loves our country and he wants to save it from people that want to destroy it.”

Kellyanne Conway was there, too, as well as a 101-year-old World War II veteran who, Mr. Trump declared, looked “a hell of a lot better than Biden.”

A day earlier, Mr. Trump had been celebrated by a group that has not always been as loyal as Club 47: Republican lawmakers. At a meeting on Capitol Hill, House Republicans serenaded him, and G.O.P. senators presented a vanilla-frosted cake with big “45” and “47” candles stuck into it.

But there is something about turning 78 that makes a man contemplate his mortality. At the rally in Las Vegas, Mr. Trump had, in a rare moment of introspection, riffed about his old age.

“My father lived a long time, my mother lived a long time, and they were happy, and they were great,” he said, sounding a bit muted. “So maybe we’re going to live a long time. I hope so.”