As religion takes an ever-higher profile in America’s national-security concerns, the FBI will play a crucial role in determining how groups are treated. I spoke with Weitzman about the history of the FBI and religion, and why this history is relevant today. Our conversation has been condensed and edited for clarity.

Emma Green: How did 9/11 change the relationship between the FBI and religious groups?

Stephen Weitzman: What 9/11 changed, to some degree, was the mission of the FBI. Prior to 9/11, its role was investigative: It was trying to stop criminal behavior and arrest criminals. After 9/11, the FBI was charged with preempting crime, or detecting it before it happened, which meant that it needed to engage in new forms of intelligence gathering. That put a new pressure on the FBI and incentivized it to behave in ways that it wouldn’t have behaved in previous decades.

Green: But as the book details, the FBI actually has a long history of investigating Muslim groups, such as the Nation of Islam and the Moorish Temple. What were some of the reasons for its investigations of those groups?

Weitzman: The Moorish Science Temple of America refers to an African American Muslim community that developed in the ’30s and ’40s. One commonality between their situation and the situation of contemporary Muslims is war. Whether you’re talking about World War II, or the war against terrorism, it creates a context in which the FBI seems to get more intrusive in its relationship with religious communities.

The larger context in the ’50s and ’60s is the Cold War. During the Cold War, the federal government came to be suspicious of certain religious groups—not just the Nation of Islam, but Martin Luther King and the movement that he led. These were seen to be, in some cases, dupes of communism. Religion was seen as a pretense by which people who had criminal or traitorous intentions were trying to legitimize what they were doing.

In some corners of contemporary society, there’s a similar suspicion of Islam as some kind of religious pretext or cover for criminal behavior. There’s a continuity in attitude and rhetoric between how the government once treated people suspected of having a collusive relationship with communism and how the government interacts with people suspected of links to terrorism.

Green: The FBI had an interesting relationship with Christian groups. With some clergy and leaders, it had strong alliances, but it also investigated and opposed a number of Christian individuals and organizations. Especially in the Cold War era, how did the FBI’s relationship with Christian groups develop?

Weitzman: A major character in that story is J. Edgar Hoover himself, who was a former Sunday School teacher. He depicted the Cold War as a spiritual struggle. He allied America and democracy with a Judeo-Christian tradition—which was an artificial construction, but he saw it as the foundation of American values.