Last October, Attorney General William Barr appeared at Notre Dame Law School to make a case for ideological warfare. Before an assembly of students and faculty, Barr claimed that the “organized destruction” of religion was under way in the United States. “Secularists, and their allies among the ‘progressives,’ have marshalled all the force of mass communications, popular culture, the entertainment industry, and academia in an unremitting assault on religion and traditional values,” he said. Barr, a conservative Catholic, blamed the spread of “secularism and moral relativism” for a rise in “virtually every measure of social pathology”—from the “wreckage of the family” to “record levels of depression and mental illness, dispirited young people, soaring suicide rates, increasing numbers of angry and alienated young males, an increase in senseless violence, and a deadly drug epidemic.”

The speech was less a staid legal lecture than a catalogue of grievances accumulated since the Reagan era, when Barr first enlisted in the culture wars. It included a series of contentious claims. He argued, for example, that the Founders of the United States saw religion as essential to democracy. “In the Framers’ view, free government was only suitable and sustainable for a religious people—a people who recognized that there was a transcendent moral order,” he said. Barr ended his address by urging his listeners to resist the “constant seductions of our contemporary society” and launch a “moral renaissance.”

Donald Trump does not share Barr’s long-standing concern about the role of religion in civic life. (Though he often says that the Bible is his favorite book, when he was asked which Testament he preferred, he answered, “The whole Bible is incredible.”) What the two men have in common is a sense of being surrounded by a hostile insurgency. A few days after Barr’s speech, Trump told an audience at the conservative Values Voter Summit, “Extreme left-wing radicals, both inside and outside government, are determined to shred our Constitution and eradicate the beliefs we all cherish. They are trying to hound you from the workplace, expel you from the public square, and weaken the American family, and indoctrinate our children.” As the effort to remove the President has gathered strength, Barr’s and Trump’s political interests have converged. Both men combine the pro-business instincts of traditional Republicans with a focus on culture clash and grievance. Both believe that any constraint on Presidential power weakens the United States.

Eleven months after being sworn in, Barr is the most feared, criticized, and effective member of Trump’s Cabinet. Like no Attorney General since the Watergate era, he has acted as the President’s political sword and shield. When the special counsel Robert Mueller released the findings of his inquiry into connections between Trump’s 2016 campaign and Russia, Barr presented a sanitized four-page summary before the report was made public, which the President used to declare himself cleared. At the behest of the President, Barr launched an investigation of the F.B.I.’s Trump-Russia probe and the intelligence community’s assessment that Russia intervened on Trump’s behalf in the election. Rather than seek a nonpartisan commission, Barr appointed a federal prosecutor, reinforcing the President’s claims of a “coup.” When an exhaustive review by the Justice Department’s inspector general found no evidence of political bias in the F.B.I. investigation, Barr issued a statement misrepresenting its findings and arguing that the evidence in the Russia probe was “consistently exculpatory”—leaving out the fact that five people connected to Trump’s campaign have been indicted for lying to investigators.

Barr maintains that Article II of the Constitution gives a President control of all executive-branch agencies, without restriction; in practice, this means that Trump would be within his rights to oversee an investigation into his own misconduct. (Barr declined multiple interview requests.) Throughout the House’s impeachment inquiry, Trump dismissed subpoenas for documents and testimony from Administration officials—a step taken by no other President. Barr and Pat Cipollone, a White House lawyer who once worked as Barr’s speechwriter, have also rejected subpoenas, flouting a congressional power plainly delineated in the Constitution. Donald Ayer, who served as Deputy Attorney General under George H. W. Bush, said, “They take the position that they don’t even have to show up. That’s totally outrageous. It’s denying the legitimacy of another branch of government in the name of executive supremacy.” Ayer described Barr’s ideas about Presidential power as “chilling” and “deeply disturbing.” If Trump survives a trial in the Senate, a President’s ability to resist congressional oversight will vastly expand. Laurence Tribe, a professor of constitutional law at Harvard, warned that Barr’s and Trump’s efforts could permanently alter the balance of power among the branches of American government. “If those views take hold, we will have lost what was won in the Revolution—we will have a Chief Executive who is more powerful than the king,” Tribe said. “That will be a disaster for the survival of the Republic.”

At the age of sixty-nine, Barr is grayer, heavier, wealthier, and more combative than he was when he served as George H. W. Bush’s Attorney General, twenty-eight years ago. But his ideology has not changed much, according to friends and former colleagues. “I don’t know why anyone is surprised by his views,” Jack Goldsmith, a law professor who headed the Justice Department’s Office of Legal Counsel during the George W. Bush Administration, told me. “He has always had a broad view of executive power.”

A longtime member of the capital’s legal establishment, Barr is described by both allies and adversaries as a formidable thinker who relishes debating issues of Roman history, Christian theology, and modern morality. During his first tenure as Attorney General, he earned the nickname Rage and Cave: when he felt that his principles had been violated, he tended to bluster, then gradually accept the situation. Colleagues describe him as both supportive and self-regarding, happy to delegate but impatient with incompetence. A self-styled polymath, Barr has strong opinions on issues ranging from legal arcana to the proper mustard to apply to a sandwich. He designed his own home, a sprawling house in McLean, Virginia, and is not above boasting about it. During a trip to Scotland with a friend, he quizzed the owner of a local inn about whether the paint on the wall was “Card Room Green or Green Smoke, by Farrow & Ball.” The innkeeper had no idea what he was talking about.

Like other prominent conservatives, Barr formed his politics in reaction to a liberal consensus around him. He grew up on Riverside Drive, in Manhattan, among the bookish élite of the Upper West Side. As his neighbors hoped that Lyndon Johnson’s Great Society would flourish, the Barr family supported Barry Goldwater for President.

Barr’s mother, Mary, taught at Columbia, and worked as an editor at Redbook. His father, Donald, was the headmaster at Dalton, a progressive private school on the Upper East Side. During the Second World War, Donald had served in the Office of Strategic Services, the precursor to the C.I.A. As headmaster, he believed that discipline instilled morality, helping to fend off the “social pathology” that his son warned about decades later. While birth control and feminism were reshaping conventions around sex and work, Donald insisted on the old ways. Chip Fisher, who attended Dalton at the time, remembered him as brilliant but out of place: “It was like having Jonathan Edwards at the pulpit.” Dalton parents saw Barr as autocratic, insular, and obsessed with adherence to rules. In the early seventies, after a protracted and ugly public fight with the school’s board, he was forced out of his job.