WASHINGTON — Late last month, more than 100 people gathered at the National Constitution Center in Philadelphia for a formal dinner featuring Justice Samuel Alito.

The gathering of the justice’s former law clerks, academics and an array of conservative federal judges considered possible contenders to succeed him was intended to mark Alito’s 20 years at the Supreme Court, a milestone he reached this year.

But according to multiple attendees, there was one topic none of Alito’s fans and acolytes raised publicly: whether the justice will serve a 21st year.

Ever since President Donald Trump returned to the White House, speculation has swirled about whether he will have an opportunity to name a fourth or even a fifth justice to the bench, which includes three justices nominated by Trump during his first term. Those questions have mounted in recent months as Trump’s political fortunes have waned and the chance that Democrats might win the Senate in November has grown.

Justice Clarence Thomas, who at 77 is the court’s oldest current justice, has over the years ruled out retiring, indicating he intends to serve for decades more. Thomas could set the record as the longest-serving justice in the Supreme Court’s history if he stays through spring 2028.

As a result, the spotlight has been trained on the court’s second-oldest member, Alito, who turned 76 this month.

The speculation has surged since Alito proved unable to address the crowd of well-wishers in Philadelphia, falling ill during the dinner and being taken to a hospital, where he was treated for dehydration, the court said. He was back on the bench the following Monday and was one of the most active questioners during high-profile arguments this month over the Trump administration’s effort to limit the guarantee of birthright citizenship.

In interviews, Alito’s friends, former colleagues and law clerks said the justice is well aware of the political calendar and would prefer to have a Republican president choose his successor.

But even those in close contact with the justice said they are unsure about his plans. Speaking on the sensitive topic on the condition of anonymity, they said the taciturn justice has not indicated even to friends whether or when he might retire. They said they believe it is possible he has not yet made a firm decision.

Alito did not respond to a request to discuss his plans.

The day after Trump was reelected in 2024, Ed Whelan, a prominent conservative legal commentator, predicted that Alito would retire in spring 2025 and that Thomas would follow this year, giving the president a chance to lock in a conservative supermajority for years.

Whelan said in an interview this past week that his predictions prompted strong pushback from close allies of the justices, and he would now be surprised if there is a vacancy this year. For Alito, he said, there are so many big cases at the court, and he has “the potential to be in the majority in a way that he couldn’t count on in his first dozen years” on the bench.

A nominee of President George W. Bush, Alito joined the court in 2005. He replaced moderate Justice Sandra Day O’Connor, making Justice Anthony M. Kennedy a critical swing vote in cases involving gay rights, abortion and the death penalty.

After Kennedy’s retirement, Alito helped move the court steadily to the right. In 2022, he wrote the majority opinion in Dobbs v. Jackson Women’s Health Organization, which overturned Roe v. Wade and eliminated the nationwide right to abortion. This term, the court is confronting a series of cases testing the legality of Trump’s policies and efforts to expand presidential power.

“I wouldn’t be surprised if he finds this a most interesting time to be there,” Whelan said. “So why leave now?”

A big potential reason is the election calendar. To varying degrees, justices want to be succeeded by someone who shares their judicial philosophy and ideology, and they consider a host of factors, including who will name their successor and the makeup of the Senate that would be asked to confirm the pick.

Months before his retirement announcement, Justice Stephen Breyer said he was struggling to decide when to hang up his robe.

“There are many things that go into a retirement decision,” he said in a 2021 interview with The New York Times, in which he recalled that Justice Antonin Scalia had said he didn’t “want somebody appointed who will just reverse everything I’ve done for the last 25 years.”

If Democrats took control of the Senate after elections in November, Trump would most likely have a difficult time getting a nominee confirmed before the end of his term. And if a Democrat were elected to succeed Trump as president, Alito would be in his 80s before there would be any chance a Republican might be back in office to name his replacement.

Many observers of the court see a cautionary tale in Justice Ruth Bader Ginsburg’s decision not to retire before the 2016 election, when President Barack Obama could have named the liberal icon’s successor. Instead, Trump nominated conservative Justice Amy Coney Barrett after Ginsburg died while in office in 2020.

All of those factors might propel a decision to leave soon, while Republicans hold 53 Senate seats.

But people close to Alito warn a decision about when to retire is highly personal.

Retiring justices sometimes announce their retirements on the last day of the court’s term, in late June or early July, but there is no requirement that they do so.

Others have suggested that his wife may be urging him to retire. Martha-Ann Alito has never been particularly fond of Washington after finding her husband’s confirmation hearings bruising.

In 2024, Martha-Ann Alito also indicated that she would have a greater ability to express her own opinions when her husband was “free of this nonsense,” comments captured in an unusual secret recording of the justice and his wife by a liberal documentary filmmaker at the Supreme Court Historical Society’s annual dinner. It is not clear if she was referring to his possible retirement.

Akhil Reed Amar, a Yale Law School professor who is friendly with the Alitos and attended the dinner in Philadelphia, said criticism leveled at the justice “may wear on him a bit.” (In 2024, the Times reported that flags that have been associated with 2020 election deniers were flown outside of Alito’s residences, spurring significant scrutiny of the justice and his wife.) But Amar said he had not asked Alito about his plans.

“I hope he doesn’t, but he might,” he said. “I don’t want him to retire because I still think he has a lot to offer.”

Although there is no current vacancy, the last three presidents have had an opening to fill within their first two years in office.

A White House official declined to comment.