“Fire the top ranks of the F.B.I.” Encourage Congress to demand testimony exposing “every single bit of filth and corruption” at the agency, and withhold its funding “until the documents come in.” Prosecute leakers and journalists. Replace the national security work force with “people who won’t undermine the president’s agenda.”

These are among a long list of changes Kash Patel recommended in his 2023 book, “Government Gangsters.” President-elect Donald J. Trump has now said he intends to make Mr. Patel the next F.B.I. director.

Mr. Trump had wanted to install Mr. Patel as deputy F.B.I. director during his first term, but Attorney General William P. Barr, who portrayed him as manifestly unqualified in his own memoir, told the White House that Mr. Patel would become deputy F.B.I. director “over my dead body.”

Mr. Barr has since been banished from Mr. Trump’s circle, and Mr. Patel’s book and other past statements are coming under fresh scrutiny as a guide to his aspirations. Some of what he has said is hyperbole, but other things would be within his power should he be confirmed by the Senate.

Charles Kupperman, deputy national security adviser during the first Trump administration, warned that Mr. Patel’s ideas would be anathema to the F.B.I.’s mission.

“The irony of this is that they all complained about the politicization of the F.B.I., and here Trump is putting in someone who’s going to do just that,” Mr. Kupperman said in an interview. “These are not reforms, they are punitive measures from a guy trying to be the enforcer for Trump.”