President Trump has chosen his first nominee, but it remains Justice Anthony M. Kennedy’s Supreme Court. The question is how much longer he wants it.

Kennedy, 80 and celebrating his 29th year on the court this month, will remain the pivotal member of the court no matter how the warfare between Republicans and Democrats plays out. On almost every big social issue, neither the court’s liberal, Democratic-appointed justices nor Kennedy’s fellow ­Republican-appointed conservative colleagues can prevail without him.

[For conservatives, a year of letdown at the Supreme Court]

That is why an undercurrent of Trump’s first choice for the court was whether it would soothe Kennedy, making him feel secure enough to retire and let this president choose the person who would succeed him.

(Victoria Walker/The Washington Post)

“Justice Kennedy tries not to play politics with these things,” said one of Kennedy’s former clerks, who watches the court carefully. Like others, he would not talk for attribution about his old boss. “But obviously he will feel more comfortable if the person who is picked is someone he likes and respects, just as the opposite would give him pause.”

Who better, then, to put Kennedy at ease than one of his former clerks? Kennedy trekked to Denver to swear in his protege Neil Gorsuch on the appeals court 10 years ago. If Gorsuch is confirmed to the Supreme Court, it would be the first time that a justice has served with a former clerk.

Gorsuch on Tuesday evening praised the “incredibly welcoming and gracious” Kennedy, along with his other judicial mentors, the late justice Byron White and Judge David B. Sentelle of the U.S. Court of Appeals for the D.C. Circuit. “These judges brought me up in the law,” he said. “Truly I would not be here without them.”

Trump campaigned for office expertly on the Supreme Court, which is especially important to conservatives and evangelicals. He went so far as to say that even if voters did not like him, they had no choice but to support him because of the potential to shape the court for a generation.

Justice Ruth Bader Ginsburg is 83, and Justice Stephen G. Breyer is 78. They are two of the court’s four liberals and are not likely to leave the court voluntarily while Trump is in charge.

Some say Kennedy would be reluctant to leave, too, if it meant a more conservative court that would reverse some of his landmark decisions, especially on gay rights. But others who know him suggest he is ready to go.

“I would put it at 50-50 that he leaves at the end of the term,” said another former clerk. Kennedy recently hired clerks for the term that begins in October, but that is seen more as insurance than intent.

(Victoria Walker/The Washington Post)

The gentlemanly Kennedy could not be more different from the combative Trump, and so some involved in filling the current Supreme Court opening kept the justice in mind during the process.

Pleasing Kennedy is wise but not dispositive, as lawyers at the court like to say.

“I suppose he’s more focused on the Trump administration as a whole,” said another former clerk. “I think that will be more important to him than whether he likes this particular pick or not.”

All agree that it will not be Trump’s first Supreme Court pick who will seal the court’s ideological direction for a generation. It will be, if it happens, his second.

Gorsuch, like almost anyone on Trump’s list of 21 candidates to take Antonin Scalia’s spot, is likely to replicate the late justice’s voting pattern (if not his style). That would restore the court’s long-held position as a generally conservative body capable of the occasional liberal surprise.

Those surprises are almost always supplied by Kennedy, nominated to the court by fellow Californian Ronald Reagan. Overall, Kennedy most often votes with the court’s conservatives: He is further to the right on law-and-order issues than Scalia was, he is comfortable with the court’s protective view of business, and he shared the losing view that the entire Affordable Care Act is unconstitutional.

But when the court moves left, it is because Kennedy joins its liberals — Ginsburg, Breyer, and Justices Sonia Sotomayor and Elena Kagan.

So Gorsuch’s appointment would return the court to the status quo that existed before Scalia died. After that, the court’s next appointment could mean a definitive shift.

The Supreme Court without Breyer, Ginsburg or Kennedy would be a different place, indeed. They have been part of the scant majority that forbade the death penalty for minors and the intellectually disabled, and established a constitutional right for same-sex couples to marry. When environmentalists win, which is becoming increasingly rare, it is because this group has banded together.

Just last term, Kennedy and the liberals struck down a Texas law that they said used protecting women as a pretext for making abortion unavailable, and they continued a limited endorsement of affirmative action.

Many if not all of those holdings would be at risk in a court with five consistent conservatives, the oldest being 68-year-old Justice Clarence Thomas.

Kennedy’s role was especially important this past term. Before writing his opinion in the University of Texas affirmative-

action case, Kennedy had never approved of a race-conscious program, although he had not been as willing as his colleagues to outlaw the use of race in such instances.

And prior to striking down the Texas abortion law, he had disapproved of only one statute on the issue — requiring a woman to inform her husband of her decision to have the procedure — among dozens the court had reviewed.

As had happened so many times before, Kennedy had the biggest impact on the most important cases. How long that continues is bigger than the current opening.