It goes almost without saying that Kash Patel, whom Donald Trump picked over the weekend to lead the F.B.I., is supremely unqualified to direct the nation’s premier federal law enforcement agency.

That’s what even those who know Mr. Patel well are saying. “He’s absolutely unqualified for this job. He’s untrustworthy,” his supervisor in the first Trump administration, Charles Kupperman, told The Wall Street Journal. “It’s an absolute disgrace to American citizens to even consider an individual of this nature.” Mr. Kupperman’s view is hardly an outlier. In Mr. Trump’s first term, Bill Barr, then the attorney general, and Gina Haspel, then the C.I.A. director, went to great lengths to prevent Mr. Patel from being installed in senior intelligence and law enforcement roles.

Patel’s selection stands out as more concretely dangerous and worrisome than many of Mr. Trump’s other questionable choices. The true danger is almost less about Mr. Patel and more about what it says about Mr. Trump and his approach to his new presidency.

To understand the full scope of the damage Mr. Patel could inflict, you have to understand how uniquely powerful and dangerous the F.B.I. can be — and why a Patel directorship would probably corrupt and bend the institution for decades, even if he served only a few years.

Choosing anyone new at this point is concerning because it is a flagrant break with tradition. There is no vacancy at the head of the F.B.I. After J. Edgar Hoover’s decades-long tenure, Congress set into law in 1976 a 10-year term for the F.B.I. director, fireable only for cause. It is meant to isolate the job from political influence, and Christopher Wray — nominated by Mr. Trump in 2017 — still has two years left to serve.

Before Mr. Trump, no incoming president had replaced the F.B.I. director on a whim; it’s a role that’s meant to exist outside the normal structure of political appointments. He now wants to fire and replace the man he selected to lead the institution because he seems to believe that Mr. Wray, a longtime Republican official, is not sufficiently loyal or willing to wield the bureau’s immense powers against Mr. Trump’s political opponents and perceived domestic enemies.

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