Fifteen minutes was all it took to show why Justice Anthony Kennedy remains a power on the U.S. Supreme Court when he provided decisive double-play votes last week,

Sitting with his seven colleagues on the bench last Thursday, the senior associate justice was finishing reading a portion of his key ruling to keep in place the University of Texas' admission criteria, which takes race into account as one of many factors to ensure a diverse campus.

"It remains an enduring challenge to our nation's education system to reconcile the pursuit of diversity with the constitutional promise of equal treatment and dignity,” concluded Kennedy in his low-key clipped voice.

Then just before the public session was over, another bombshell: the court dealt a setback to President Obama's unilateral executive action on immigration.

The 4-4 ruling, where Kennedy this time backed his right-leaning colleagues, was a victory for states and the GOP Congress that opposed the administration's plan to shield millions of undocumented aliens from possible deportation.

Four days later, on the last public session before the summer recess, the final dramatic act: the court by a 5-3 vote struck down a Texas law imposing tough regulations on clinics performing abortions.

Kennedy, pivoting again to the left, was the deciding factor to conclude the regulations placed an "undue burden" on women seeking access to the medical procedure, affirming earlier precedent that Kennedy himself helped establish.

Now more than ever, the court's unapologetic "swing vote" is quietly flexing his judicial power on a dizzying mix of hot-button cases.

That has been particularly true since his friend and conservative colleague Antonin Scalia passed away in February, leaving the court short-handed for the foreseeable future.

Republicans in the Senate have vowed not to confirm Obama's nominee-- Judge Merrick Garland-- leaving the possibility the seat will remain unfilled until next year, when the next President would choose

It has left a strategic void that makes Kennedy's unique jurisprudence that much more coveted among his colleagues. Amid uncertainty, he quietly thrives.

Do the math: the four reliable liberals and three reliable conservatives now orbit around Kennedy's moderate-conservative credentials, knowing he almost inevitably will provide the crucial deciding vote.  While the justice mostly holds to the right, he can move comfortably away when he sees fit.

"The basic principle is, it is Justice Kennedy's world and you just live in it," said Thomas Goldstein, a private appellate attorney and creator of scotusblog.com. "On a court of nine members there almost has to be someone in the middle by definition.  His job where he sits on this court is to cast the deciding vote sometimes."

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After the recent abortion and affirmative action decisions, many political conservatives are now lamenting that Kennedy, who turns 80 this month,” may be a “lost cause,” since he had previously sided with the right to a large extent on these issues.

The fear on the right is that with the election of a Democratic president, Scalia's replacement would be poised to establish a solid five-vote liberal majority, breaking a quarter-century or more lock held by the right. In order to preserve his crucial role, some legal experts think Kennedy may be setting the groundwork to go left and stay there, hoping to lead that bloc in his final years on the bench.

"Increasingly we are seeing him swinging to the left more and more, this has been really evident in the last few terms where we have seen liberals get historic victories," in cases including same-sex marriage, said Carrie Severino, chief counsel at the Judicial Crisis Network.

She told Fox News that despite a reputation as defending states’ rights over federal control.

"I think we see increasingly Justice Kennedy is willing to abandon some those core principles of the constitutional system when it comes to achieving liberal policy goals, and that is discouraging to see."

But other court watchers-- especially those who know him personally-- think Kennedy will continue to be Kennedy: unpredictably influential and invested on both sides. Many associates deny he is agenda- or legacy-driven.

The justice has crafted a powerful, if hard to define, judicial power base-- seemingly in the forefront of every major ruling during his tenure. He was the key behind-the-scenes architect of the 2000 Bush v. Gore drama, a 1992 opinion upholding abortion rights, and perhaps his crowning achievement, last year's decision legalizing same-sex marriage.

Kennedy's "Greatest Hits" as the key author or swing vote on the high court could fill multiple volumes. He has written majority decisions on campaign spending laws, underage killers, and foreign fighters held by the U-S military in the war on terror.

And along with Justice Sandra Day O'Connor, the two native westerners carved out a jumpy place in the center, before she stepped down a decade ago.

Less driven by practical concerns than O'Connor, Kennedy has striven for a loftier sense of the law's impact on society, such as a 1992 opinion affirming Roe v. Wade, but allowing for "reasonable" state restrictions: "At the heart of liberty is the right to define one's own concept of existence, of meaning, of the universe, and of the mystery of human life."

That earned him nicknames inside and out of the court: Flipper, Errant Voyager, Man in the Muddle. Kennedy's complex, some say unique, views on the law leave little room for consensus among his supporters and detractors. His rulings have been described as both inspired and grandiloquent.

"Justice Kennedy is a man who really doesn't know his own mind," said Douglas Kmiec, a former Justice Department lawyer who helped formally vet Kennedy to the high court in 1987. "And that's not meant entirely as a criticism, because the positive way to say that is: he's open-minded."

"He has not been a justice to look at overarching principles, one rule that settles every case," said Orin Kerr, his law clerk from 2003. "His decisions are considered unpredictable because he's not always going to rule in favor of the government, he's not always going in favor of a defendant. He's going to look case by case and that makes his decisions distinctive."

He has generally supported his conservative colleagues on issues of crime, the death penalty, federalism, and civil rights. But also has backed the left on abortion, homosexual rights, and school prayer.

"These labels have meaning only relative to the other justices, so it has turned out Justice Kennedy has been in the middle of the court, pretty much since his appointment," said Nicholas Quinn Rosenkranz, his law clerk from 2001. "His judicial philosophy didn't necessarily create a clean answer to every case, so he would have to think them through case by case."

And a judicial confidence in the California native's own role, and that of the court he has shaped, has long been evident. Judges, he once said, have power and duty to "impose order on a disordered reality."

As for Kennedy himself, "sometimes people think compromise means squishy, centrist," he has said. "It doesn't."