But he's no flip-flopping political candidate; he's a lawyer. Changes like this are part of his job.
Clement is playing a key role in three politically charged Supreme Court cases in which Republican-led states object to Obama administration policies or federal laws on health care, immigration and redrawing political boundaries.
In the biggest of those, the 45-year-old law school acquaintance of President Barack Obama will be trying to sink Obama's health care overhaul.
Not that long ago, Clement would regularly stand before the justices and defend even the most aggressive uses of federal power, making his case without written notes and parrying questions with an easy banter.
He argued for the Bush administration's policy on detaining suspected terrorists, a federal law outlawing a medical procedure called "partial-birth abortion" by opponents, the McCain-Feingold law aimed at limiting the influence of money in politics and a federal ban on the use of marijuana for medical purposes.
Clement was President George W. Bush's top Supreme Court lawyer, the solicitor general, the last government job on his impeccable conservative resume. He was a law clerk for Justice Antonin Scalia, then worked for John Ashcroft, both when Ashcroft was a senator and attorney general.
If a Republican wins the White House, expect to find Clement among the top potential Supreme Court nominees, said Curt Levey, who heads the conservative Committee for Justice. "It's unimaginable that any Republican president wouldn't have him on their short list."
His recent run of cases hasn't hurt his chances.
"There's no doubt that Paul has become the leading advocate for the most deeply conservative causes in the law. That is a reputation he has worked hard to earn," said David Frederick, a Supreme Court lawyer who often represents consumers.
Clement is scheduled to argue seven cases at the high court this term, roughly 10 percent of the total and a staggering figure for a lawyer in private practice. Supreme Court lawyer Thomas Goldstein jokingly introduced Clement at a recent event as having "the distinction of arguing every case in the Supreme Court this term, or nearly so."
The last of those will be a defense of Arizona's immigration law in the face of a challenge from the White House.
He already scored at least a partial victory when the court threw out interim Texas electoral maps that were drawn by federal judges and opposed by the Republicans Clement represented.
But the centerpiece of Clement's work, and of the high court term, is the election-year fight over the law that is intended to extend health care coverage to more than 30 million people. Clement will carry the bulk of the argument among several attorneys with clients opposing the law.
Representing Florida and 25 other states, Clement's central argument is that Congress went too far in requiring nearly every American to purchase insurance or pay a penalty.
"There have been a lot of crises in this country over the years, economic, other, where Congress might have thought that forcing individuals to purchase a particular good or a particular service might have been a useful means of government action. But the government never did," he said.
Born and reared in Cedarburg, Wis., Clement was a year behind Obama at Harvard Law School and worked under him on the Harvard Law Review. He was the youngest solicitor general, at 38, in 115 years.
Clement's unassuming, buttoned-down image provides little hint of his fondness for alternative rock bands he sometimes sees at Washington's 9:30 Club. He lives in suburban Virginia with his wife and three sons.
He has maintained a heavy workload despite an upheaval in his professional life that took him from the 800-lawyer King & Spalding firm to tiny Bancroft LLC. Atlanta-based King & Spalding spent a reported $5 million to lure Clement after he left government in 2008. Clement won't confirm the figure, but he does not dispute it.
Clement easily attracted deep-pocketed clients, including National Football League owners in their dispute with players.
But his representation of House Republicans in support of the Defense of Marriage Act prompted an internal struggle at the firm. The Obama administration is no longer defending the 1996 law that defines marriage as a union between a man and woman, and prohibits the government from granting benefits to same-sex couples.
King & Spalding eventually withdrew from the case, leaving Clement in the uncomfortable position of having to quit his clients or the firm. He chose the latter, which drew criticism from some gay rights groups but praise from lawyers across the political spectrum, including Justice Elena Kagan, an Obama nominee to the Supreme Court.
At Georgetown University last year, Kagan spoke of Clement's "integrity, professionalism and honor" and said Clement's critics "misunderstand the traditions and ethics of the legal profession."
Clement himself says the experience bolstered his view that he would not choose clients out of fear of taking on unpopular causes. "It seems like a formula for a really uninteresting legal practice," he said.
And despite his ties to Republicans, Clement insists that when he stands before any court, "you have to really buy into the notion that positions are taken on behalf of a client. They're not your positions."
He notes that he has been on the liberal side sometimes -- arguing for California prison inmates seeking better medical and mental health care and seeking higher fees for lawyers who won changes in Georgia's foster care program.
Still, when he left King & Spalding, he, along with many of his clients, ended up at Bancroft, run by Harvard law classmate Viet Dinh. The 13-lawyer firm is heavy with former Bush administration officials, including Dinh, and law clerks to Chief Justice John Roberts.
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