We tend to think of Hoover as a one-dimensional villain and a rogue actor — essentially, as someone who operated outside of normal checks and constraints. It’s true that Hoover often acted in secret, with little accountability. But he could not have remained FBI director for an astonishing forty-eight years without having some other skills as well.

He was a consummate bureaucrat who came of age with an expanding federal government. He made his name espousing many of the key values of the progressive state: efficiency, objectivity, professionalism, scientific methods. Though we rarely think of him this way, those ideas helped to make him enormously popular, both inside and outside of Washington. We can’t understand his career or his influence without taking that “administrative” story into account.

Anti-communism was the great cause of Hoover’s life. He viewed that cause expansively: as a national security matter, but also as an existential struggle for the country’s soul. In 1919, at the tender age of twenty-four, he became the first head of the Justice Department’s new Radical Division, which pioneered techniques of surveillance and deportation aimed at left-wing radicals. But his greatest influence came in the 1940s and 1950s, when he became the nation’s most famous and best-respected anti-communist.

We tend to think of Joe McCarthy as the figurehead of the Red Scare, but Hoover was far more influential. He was there before McCarthy, establishing new surveillance operations and working with congressional committees — even the White House — to manage the Red Scare’s political side. And he outlasted McCarthy, too. McCarthy died in 1957, but Hoover survived to carry many Red Scare techniques into the 1960s, when he targeted civil rights activists, the antiwar movement, and the New Left.

Hoover’s close relationship with liberals — and with liberalism — fascinated me as I worked on the book. Though Hoover was appointed director of the Bureau of Investigation (forerunner of the FBI) in 1924, it was really Franklin Roosevelt who gave him much of his power.

Under Roosevelt, FBI agents expanded their role in federal law enforcement, becoming the great heroes of the New Deal’s War on Crime. During World War II, they expanded again, this time into a national domestic intelligence force. Roosevelt also taught Hoover how to sell the FBI’s work to the public. Both men believed that the work of government was not self-evident, that the American people had to be shown and taught to have faith in federal power.

Lyndon Johnson embraced Hoover, too. In 1964, he exempted Hoover from mandatory federal retirement at the age of seventy, a key decision that allowed Hoover to stay in power throughout the critical years of the late 1960s and early 1970s. Throughout his presidency, Johnson used Hoover in a variety of ways — often to contain the Civil Rights Movement, on occasion to empower it. The most outrageous FBI operation of the 1960s, its campaign of harassment and surveillance aimed at Rev. Dr. Martin Luther King, Jr., took place with Johnson’s knowledge and support, even if Johnson did not necessarily know every detail of what the FBI was doing.

We might think of Hoover’s relationships with these liberal titans as strange or anomalous, because we know Hoover best for his conservative social views. But it makes sense that figures like Roosevelt and Johnson, famous for their ambitions and their willingness to use the power of the state, would admire a skilled state-builder like Hoover. Those relationships also highlight the ways that liberals in power have often been suspicious of the Left and have supported efforts to contain and discredit left-wing groups.

Hoover’s racism is well-known. What I wanted to do in this book was tell a slightly more complicated story about how that racism worked in practice. One influential factor was his membership in Kappa Alpha, his college fraternity, which was explicitly devoted to advancing the “Lost Cause” of the white South.

Hoover chose many first-generation FBI officials from in and around Kappa Alpha, helping to create an institutional culture based on segregationist views and values. As director, he expended enormous time and effort targeting civil rights sympathizers, ranging from the National Association for the Advancement of Colored People (NAACP) and King’s Southern Christian Leadership Conference (SCLC) to the Student Nonviolent Coordinating Committee (SNCC) and the Black Panthers. He often justified those efforts not in explicitly racial terms, but by pointing to the suspicion that civil rights groups might have been infiltrated by communists — or even just that communists sympathized with racial-justice movements, thus making all of them suspect.

There was also a lot of overlap in FBI techniques pioneered against the Communist Party and later applied to civil rights groups. The most famous is COINTELPRO (which stands for counterintelligence program). COINTELPRO started a campaign of harassment and disruption aimed at the Communist Party. As the 1960s went on, though, it expanded to include a vast array of civil rights and Black Power groups, as well as particular figures like King and Carmichael.

The American far right loved Hoover, but he did not always love it back. Hoover was a hero to many far-right organizations, including the John Birch Society, for his outspoken conservative views on crime, race, religion, and communism. He welcomed some of their support, cultivating groups like the American Legion and the Daughters of the American Revolution as part of the FBI’s grassroots constituency.

But he was also often suspicious of right-wing groups for their conspiratorial, far-fetched thinking and their vigilante impulses. Hoover always thought that the work of rooting out threats to the social order ought to be left to the professionals at the FBI, and he disliked groups that tried to take such matters into their own hands. He especially disliked violent right-wing and white supremacist groups like the Ku Klux Klan, who often thumbed their noses at federal authority.

Those views sometimes led to surprising results. In the 1940s, the FBI launched a reasonably serious attempt to contain lynching in the South, in part because Hoover thought that lynching undermined federal authority and the politics of “law and order.” In the 1960s, he launched a set of COINTELPRO operations against the Klan and other white supremacist and neo-Nazi groups under a similar logic. He never conducted those operations with the same energy and enthusiasm he applied to campaigns against the Left, but they were still substantial operations. From a biographical perspective, they help to make Hoover a more complicated figure.

At the same time, the imbalance between the FBI’s campaigns against the Right and Left calls into question one of the more cherished myths of the mid-century conservative movement: that they were the consummate outsiders in an age of liberal consensus. It’s hard to say you’re really an outsider if the head of the nation’s political police agrees with many of your views.

Liberals now love the FBI! Some do, anyway. Polls show that Democrats on the whole are now far more supportive of the FBI than Republicans are. Most of that has to do with Trump, of course. But it’s also a reversion to an earlier period in FBI history, when liberals admired and empowered Hoover — and for some of the same reasons we see today. Though Trump is the key point of contention, defenders of the FBI now point to its designated role as an objective, nonpartisan, investigative force loyal to the facts and to the law — the most noble part of the FBI’s history and traditions.

Of course, today’s liberals may be making some of the same mistakes that mid-century liberals did: In supporting the FBI, they may be ignoring possible excesses and abuses. That’s one of many areas where Hoover’s example ought to be instructive.