(CNN) When Anthony Kennedy was sworn in at the White House in February 1988, President Ronald Reagan heartily congratulated new "Justice Kennedy" and quipped, "Sounds good, doesn't it?"

It did and it has.

Kennedy has always reveled in his place on the Supreme Court and his role interpreting the Constitution, which he proclaimed at that East Room ceremony 30 years ago "the single fact, the single reality, the singe idea, the single moral principle, that sets the United States apart from other nations now and throughout history."

And that might be one reason the 81-year-old Kennedy, under a media microscope for any signs of an imminent retirement, decides not to step down at the end of the session in June.

Often casting the deciding vote on this sharply divided court, Kennedy is evasive when asked about his plans. Yet he may be finding more reasons to stay than go, beginning with the fact that he has always lived for this.

Constitutional Exuberance

The Sacramento native who taught law school while serving first on a US appeals court has remained as animated about constitutional issues as he was when he approached the microphone 30 years ago with two thumbs up. He is known for his lofty rhetoric, sometimes drawing criticism from dissenting colleagues for being over-the-top. Elevated references to individual dignity and equality marked his opinions as he broke ground on gay rights and same-sex marriage over the years.

But even this week in a car-search dispute, Kennedy spoke grandly: "Few protections are as essential to individual liberty as the right to be free from unreasonable searches and seizures. The Framers made that right explicit in the Bill of Rights following their experience with the indignities and invasions of privacy."

In opinions and in speeches, Kennedy rarely passes up a chance to hail the document that he still holds up as defining America.

He gets to write the big opinions

Kennedy, a centrist conservative, is more than "the decider," as he has been dubbed because he often casts the crucial fifth vote on the nine-member bench. He writes many of the most consequential opinions. This longest serving sitting justice is second in rank only to Chief Justice John Roberts.

When Kennedy joins the four liberals for a majority decision, his seniority give him the power to assign the opinion. He routinely keeps the case for himself. When he aligns with the four conservatives (Roberts included), Kennedy's vote is usually needed to hold the majority. So Roberts often assigns him the opinion to ensure that he stays with that fivesome and is not dissuaded by the reasoning of a justice further to the right.

Centrist vote matters more on this divided court

Kennedy is more relevant now than if President Barack Obama's nominee Merrick Garland had been confirmed in 2016, or if Democratic presidential candidate Hillary Clinton had won the election and in 2017 filled the vacancy left by the late Justice Antonin Scalia. (Scalia died in February 2016, and the court was at eight justices for more than a year.)

It was during this period that Kennedy began seriously mulling retirement. He was nearing 80 yet perhaps also thinking that the addition of a fifth liberal would diminish the force of his centrism. When Donald Trump won the election and then chose conservative Neil Gorsuch, Kennedy regained his place in the middle.

Trump era brings big cases

The Supreme Court could be entering an especially significant era, with Trump forging a new legal agenda and poised for confrontations with special counsel Robert Mueller, investigating any Trump campaign connection to Russia's interference in the 2016 election.

The justices might have to resolve whether a president could be forced to testify before a grand jury or could be indicted at some point. Such possibilities are even more speculative than what might be in the mind of the often-vacillating Kennedy. Still, large constitutional questions loom, and Kennedy might want to be there.

Hard job to give up

Justices, appointed for life, resist retirement. Two of the last five justices to leave the bench died in office. William Rehnquist thought he could survive another year with thyroid cancer but succumbed to the disease at age 80 in September 2005. Scalia died while on a hunting trip in February 2016, just weeks from turning 80. When Justice John Paul Stevens stepped down in 2010, he was 90. Breaking the pattern, Justice David Souter left the bench in 2009 at the relatively youthful age of 69. He was eager to return to a quieter life in his home state of New Hampshire. Justice Sandra Day O'Connor retired in early 2006, at 75, with mixed feelings, to take care of her ailing husband.

Kennedy's feelings on whether he stays or goes are difficult to predict. When he tackles cases, he weighs multiple options and sometimes wrings his hands even after he has decided.

In 1992, for instance, when he cast the deciding vote to reaffirm a woman's right to abortion, Kennedy told a reporter from California Lawyer magazine just before the case was to be announced: "Sometimes you don't know if you're Caesar crossing the Rubicon or Captain Queeg cutting your own tow line."