It appears in retrospect that Thomas was obscuring his views in order to win Senate votes. On the court, he became the justice most determined to use originalism to rip up whole fields of American law, especially to reduce the scope of federal regulation. “When faced with a demonstrably erroneous precedent, my rule is simple,” he wrote last June in a solo concurrence — a separate opinion agreeing with a judgment — in Gamble v. United States. “We should not follow it.” He has written solo opinions at a higher rate than any other sitting justice. When Scalia was alive, he painted Thomas as an extremist. Comparing himself with Thomas at a talk at a synagogue 15 years ago, according to the New Yorker writer Jeffrey Toobin, Scalia cracked: “I am an originalist, but I am not a nut.”

But over time, positions Thomas once floated from the margins of conservative thought have moved into its mainstream. “Justice Thomas has been throwing out revolutionary concepts for a long time now,” Yoo, his former clerk, said. “He was interested in being proved right by history, or by the court 20 or 40 years into the future. Now you could say his influence is reaching its height.” Trump officials have expressed their appreciation for Thomas, with McGahn calling his recent opinions a “driving intellectual force.” The administration has successfully nominated more than 10 of his former clerks, the highest total for any justice, to the federal bench.

In 2012, what was once Thomas’s radical originalist rationale for curtailing Congress’s powers to pass laws based on the Constitution’s Commerce Clause almost became the basis for striking down the Affordable Care Act. He first argued this position in the 1995 case United States v. Lopez, saying that when the Constitution was written, “commerce” referred only to “selling, buying and bartering, as well as transporting for these purposes.” This led to the extraordinary suggestion that the Supreme Court had been wrong to uphold the entire social safety net of the New Deal, because it involved “substantial effects” on commerce among the states. Seventeen years later, in the Affordable Care Act challenge, all five conservative justices embraced this thinking, finding that Congress had indeed exceeded its commerce powers. Only Roberts’s defection from the conservative majority, in concluding that the individual mandate was permitted by Congress’s power to tax, saved the health care law.

Thomas, who declined to talk to me, moves back and forth between different forms of originalism, sometimes focusing on the intention of the framers and sometimes on the 18th-century meaning of the words, according to Ralph Rossum, a government professor at Claremont McKenna College, in his otherwise sympathetic book, “Understanding Clarence Thomas.” Sometimes, Thomas ignores originalism altogether. For example, he provided no evidence that the First Amendment’s original meaning supported his position in a 1996 concurrence in which he argued that limiting the political donations of corporations violated their free-speech rights. The conservative majority embraced that argument 14 years later in Citizens United v. F.E.C. to strike down limits on corporate campaign donations.

In his 2019 book, “The Enigma of Clarence Thomas,” the political scientist Corey Robin traces Thomas’s version of originalism to his code of self-reliance. Thomas called his memoirs “My Grandfather’s Son,” writing with reverence about his grandfather’s achievement of lifting the family out of poverty by starting a fuel-delivery service in Georgia despite the barriers of Jim Crow. In college, Thomas was a black nationalist who followed Malcolm X, signing his letters “Power to the People.” But after law school, he became a free-market conservative. Criticizing President Franklin D. Roosevelt and other New Deal liberals in a 1987 speech for the Pacific Research Institute, a think tank, Thomas said: “These critics of ‘the rich’ really do mean to destroy people like my grandfather.” His opinions often align with his belief that the unfettered market, not government efforts to redistribute wealth or ameliorate discrimination, is “the guarantor of precisely the kind of freedom upon which the black community depended,” as Robin writes.

Thomas’s main innovation has been to deploy originalism to loose the government’s reins over the market. One advantage of originalism is that it allows conservative judges to justify sweeping away American legal traditions, like the broad power of Congress to regulate. “You have to claim to be going back to first principles,” David Strauss says. “Otherwise, it’s just that you don’t like the legal order we have.”