Angelo M. Codevilla, a conservative political theorist whose writings in the 1980s helped define the hawkish wing of the Republican Party and later, over the last decade, both predicted and gave intellectual shape to the populist revolt against the party’s establishment, died on Sept. 20 in Tracy, Calif.

His son David said the cause was a car accident, which occurred while Dr. Codevilla was returning to his vineyard near Sacramento after a medical appointment at Stanford.

Dr. Codevilla (co-deh-VILLA) first came to prominence in the early 1980s when, as an aide to Senator Malcolm Wallop, a Wyoming Republican, he was a leading advocate for a space-based antimissile system, a sharp critic of the Cold War arms control regime and a sworn enemy of the C.I.A., which he said should be broken up.

Running through much of his work, which he continued as a fellow at the Hoover Institution, at Stanford, and later at Boston University, was a belief that American foreign policy was controlled by an insular, mostly liberal elite, which suppressed dissent, promoted groupthink and hamstrung the country’s military.

“The arms control process is really about the unilateral shaping of American military forces by the American foreign policy establishment,” he and Senator Wallop wrote in their book “The Arms Control Delusion” (1987). “Any effect arms control might have on the Soviet Union is of secondary importance.”

By the late 2000s, Dr. Codevilla had extended that critique to domestic politics and its dominance by what he called the “ruling class,” a position he outlined most fully in a 2010 cover story in The American Spectator, a conservative magazine.

Contemporary class in America, he wrote, was less about money and power, let alone merit, than it was about identity. At the top sat those who had mastered the “social canon of judgments about good and evil”; everyone else — what he called the “country party” — fell below, cast aside as backward and racist.

Dr. Codevilla was far from the first to see class in such cultural terms. His contribution was to combine that analysis with a critique of big government: Whereas other observers might see America’s class inequalities as the product of educational or technological shifts, he saw them as a result of a self-reinforcing bond between progressive ideas and the growing power of the state across the 20th century.

“Regardless of what business or profession they are in,” he wrote about the ruling class, “their road up included government channels and government money because, as government has grown, its boundary with the rest of American life has become indistinct.”

While Dr. Codevilla believed that the ruling class spanned both parties, he said it was rooted on the left, which dominated academia, media and government. But because of that, he had particular scorn for the Republican establishment, which he said should be representing those outside the ruling class but instead did everything it could to accommodate it.

After the article caught the attention of Rush Limbaugh, who promoted it heavily on his radio show, a longer version was rushed into production as a book, “The Ruling Class: How They Corrupted America and What We Can Do About It” (2010).

The only solution to the ruling class’s hold on American life, Dr. Codevilla said, was a revolt against the Republican leadership for the soul of conservatism. It was a clarion call that made the article and book required reading among the Tea Party movement that swept across American politics in the early 2010s — and, a few years later, among the Trump campaign as well.

“In retrospect, he wasn’t just prescient about the Trump movement,” Daniel McCarthy, the editor of Modern Age: A Conservative Review, said in a phone interview. “Codevilla helped bring it about by diagnosing it.”

Angelo Maria Codevilla was born on May 25, 1943, in Voghera, Italy, a city about halfway between Milan and Genoa. His father, Angelo, worked in a printing business but died before he was born. In 1955 Angelo and his mother, Serena (Allemangano) Codevilla, a dressmaker, immigrated to Fort Lee, N.J.

Dr. Codevilla studied physics at Rutgers University, where he graduated in 1965, and later received a master’s degree from the University of Notre Dame and, in 1973, a doctorate in political science from the Claremont Graduate University. He served in the Navy Reserve from 1969 to 1971.

Besides his son David, he is survived by his wife, Ann Marie (Blaesser); his children Peter, Michael, Thomas and Elizabeth; and nine grandchildren.

Following a brief stint in the Foreign Service, he joined the staff of the Senate Select Committee on Intelligence in 1977, where he worked until 1985, mostly as an adviser to Senator Wallop. He was a member of the Reagan administration’s transition team, in 1980, and taught at Georgetown University.

By the time he took emeritus status at Boston University, in 2008, he had moved to Northern California, where he owned a vineyard. His intellectual output did not slow down, though. In addition to his work at The American Spectator, where he was a senior editor, he wrote regularly for leading conservative opinion outlets like The Claremont Review of Books, The Wall Street Journal, Commentary and the online journal American Greatness.

He wrote or co-wrote 17 books, including a translation of “The Prince,” by Machiavelli. A book on John Quincy Adams, one of his intellectual heroes, is due out in 2022.

Though he initially supported the U.S. invasion of Iraq, which was instigated by President George W. Bush, Dr. Codevilla soured once it turned into a nation-building effort — the product, he said, of the misbegotten belief on the part of the establishment that America must use its power to change the world rather than defend its interests.

Dr. Codevilla welcomed Donald Trump’s victory in 2016, and he felt encouraged by the president’s anti-establishment rhetoric. But he later said he was disappointed by Mr. Trump’s failure to match words with action — a failure that, he believed, had actually strengthened the ruling class by giving it an enemy to rally against.

“Trump denounced his and his supporters’ enemies, though seldom giving specific reasons for the criticism, while suffering rather than hurting them, motivating them to do their worst, and letting them do so with impunity,” he wrote in an article for American Greatness in July. “He effectively accredited the very people who were discrediting him.”

The result, he said, was a “cold civil war,” in which America was even more divided than it had been before the actual Civil War — at least then, he said, citing Abraham Lincoln, Americans worshiped the same god. Now, he argued, the country lacked even that common cultural foundation.

“Russians and East Germans under Communists Leonid Brezhnev and Erich Honecker in the 1970s lived under less ruling class pressure than do today’s Americans,” he wrote in 2019 in American Greatness. “And their rulers were smart enough not to insult them, their country, or their race.”

Dr. Codevilla was particularly incensed over the government’s response to the pandemic. He considered Covid a public-health threat on par with a bad strain of the flu, but said that the ruling class, including Dr. Anthony Fauci — whom he called a “deep state fraud” — had used it as an excuse for an unprecedented power grab.

That, he wrote in his July article, made it imperative for the next generation of Republican leaders to double down on Trumpism, to take on the ruling-class establishment in not just words but action.

“To be worthy of following, post-Trump leadership must become consistent in deed with the insight that vaulted Donald Trump to public attention,” he wrote in the July article. “Picking up where he left off is up to anyone who would succeed him at the head of America’s republicans.”