President-elect Donald Trump shocked even some of his most ardent critics when he announced he would nominate former national security aide Kash Patel to lead the FBI.

Trump called Patel a “brilliant lawyer, investigator, and ‘America First’ fighter who has spent his career exposing corruption, defending Justice, and protecting the American People” in a post on social media over the weekend.

Patel, a former Justice Department prosecutor and fierce FBI critic, openly vowed to find ways to punish Trump’s perceived enemies. Critics say that would be an appalling use of the justice system to carry out political ends.

But if that were to occur, it would not be the first time. The agency’s longest serving director, J. Edgar Hoover, authorized covert harassment campaigns against perceived enemies like the Rev. Martin Luther King Jr.

There are more guardrails on the FBI now than there were decades ago, historian and author Beverly Gage told NPR’s Michel Martin. But whether protections will be strong enough to hold up against pushes they haven’t been subjected to, as could happen under Patel, is the big question.

Gage, who wrote the Pulitzer Prize-winning G-Man: J. Edgar Hoover and the Making of the American Century, also believes the FBI’s politicization could damage the American public’s view of it even further.

She spoke to Morning Edition about what Patel’s pick means for the FBI and how the agency has in the past exerted vast amounts of power and influence, particularly under Hoover, its most notable director.

This interview has been edited for length and clarity. 

Michel Martin: What is the history of the FBI? How did it start and how did it become what a lot of people call the preeminent law enforcement agency in the United States?

Beverly Gage: The FBI got started pretty informally and actually pretty controversially during the progressive era. The Justice Department decided it needed its own investigators. This was around 1908. J. Edgar Hoover became the head of the bureau in 1924, and he’s really the one who put his stamp on it and turned it into, as you said, our premier law enforcement agency, but also our domestic intelligence agency. And those things have sometimes gone very well together and sometimes not so much.

Martin: How did it happen that he led the FBI for 48 years? I mean, that’s just inconceivable today.

Gage: Hoover came in at a moment when the government was just starting to expand in the 1920s. And he really built the bureaucracy in his own image and kind of managed its politics really successfully for almost half a century.

Martin: The fact that the FBI director has a 10-year term, which exceeds the two terms allowed to a president, was that a reaction to Hoover?

Gage: It was a reaction to Hoover. The analysis at the time in the ’60s and ’70s – he died in 1972 – was that future directors should not be able to amass that kind of power because it made Hoover sort of invulnerable.

Martin: Was there a bipartisan consensus at the time that there needed to be these kinds of controls?

Gage: Hoover served under four Democrats and four Republicans. He was pretty careful to be nonpartisan, really tried to keep the FBI out of politics because he thought it would damage the agency. He thought that it wasn’t right and he never would have done what we’re seeing today.

Martin: Liberals have long been suspicious of the FBI because of that legacy of covert harassment campaigns. When did the right start to become suspicious of the FBI?

Gage: When Hoover died in 1972, there would have been a lot of suspicion coming from the left and from liberals who were very critical about the FBI’s disruption of the civil rights movement, the antiwar movement. He was an ideological conservative, but a lot of conservatives really thought of the FBI as the part of the state that they liked. And so one of the really interesting things that’s happened certainly in the last decade is that we can see that flip around, but we’ve never seen anything like what’s been happening in the last several years, which is certainly Trump and his allies, but in large part, the mainstream Republican Party has really turned on the FBI and the national security state in a whole new way.

Martin: What do you make of Mr. Patel’s vow that he will use the levers of the justice system to punish those who he believes have unfairly targeted the president elect? Can he do that?

Gage: Look, there are a lot more controls on what the FBI can do, both legally and in terms of intelligence than there were during Hoover’s day. What Hoover did a lot of and where I think there is some more wiggle room even today, is in harassment campaigns, in wiretapping and bugging, the use of secret information. And in some ways, the great danger at the FBI is not going after people such that we’re going to end up in court. But the use of secret information, the use of the FBI’s surveillance and intelligence powers to specifically target people who are your personal enemies, your political enemies or your ideological enemies.

Martin: Well, one of the things that Hoover did is he authorized behavior that many people today look at as completely outside the boundaries, like, for example, discovering things about people’s personal lives. Are there any guardrails against that kind of conduct happening again?

Gage: There are more guardrails now than there were then. A lot of them are internal to the FBI and to the Justice Department. The question is whether they’re going to be strong enough to hold against a push that they have never been subjected to before. The major things that happened in the 1970s, after Hoover’s death, to begin to revise control, prevent the sorts of practices that went on during his time partly were about Congress. Congressional intelligence committees came into being. They had a lot more access to what was happening in the world of intelligence. There’s a little bit of law that’s now in place that looks quite different, but a lot of it was about internal reforms within the Justice Department and the FBI itself.

Martin: Which can be abrogated if the people who run that department so choose.

Gage: It does seem that that’s possible.

Martin: Do you have a sense of just what the public thinks about the FBI now?

Gage: I think that the FBI is in some real trouble with the public. The FBI’s legitimacy, its ability to do its work, its ability to have the support of the public really depended upon its nonpartisan image. And I think this latest appointment may potentially damage it even further. Trump seems to be saying, I want to use the FBI and its powers in order to go after my enemies and I want to destroy the FBI kind of from within. And he wants both of these things at once.

This article was edited by Treye Green. The radio version was edited by Adriana Gallardo and produced by Julie Depenbrock.