On Wednesday morning, at a hearing before the Senate Judiciary Committee, Senator Kamala Harris, Democrat of California, repeatedly asked Christopher Wray, the director of the F.B.I, a question: Had the White House limited the Bureau’s supplemental background investigation into sexual-abuse allegations against Brett Kavanaugh, prior to his confirmation to the Supreme Court? Wray, choosing his words carefully, confirmed that it had. “The investigation was very specific in scope, limited in scope,” he said. Wray said that he could not comment publicly, or needed more time, to answer a series of follow-up questions from Harris regarding the parameters of the investigation: Who decided that the F.B.I. would not interview Kavanaugh, Christine Blasey Ford, and dozens of other individuals with potential information about the accusations? Did the Bureau look into allegations that Kavanaugh had lied to Congress during his testimony? Did the White House counsel, Donald McGahn—Kavanaugh’s chief defender—direct any element of an F.B.I. investigation that Republicans have described as thorough and independent?

Wray’s reticence reflected a constant dilemma: Should he, in order to defend the F.B.I’s reputation, publicly criticize President Trump whenever he undermines the Bureau’s independence? The Kavanaugh probe was, indeed, limited. At the direction of the White House, it lasted just five days and included interviews with only ten people. Yet, during the nationally televised swearing-in ceremony for Kavanaugh, on Monday night, Trump told the new Justice, “You, sir, under historic scrutiny, were proven innocent.”

A former senior F.B.I. official, speaking on the condition of anonymity, said that the President is engaged in an “overt attempt to politicize law enforcement.” Since Trump took office, the former official told me, “his Administration has relentlessly worked to kneecap the Bureau at every turn, in order to subvert public confidence in the Russia investigation. With Kavanaugh, the White House reversed course, and attempted to capitalize on the F.B.I.’s good reputation to score a political win.” When reached for comment about the Kavanaugh investigation, a White House spokesperson referred The New Yorker to Wray’s testimony.

The Bureau’s wariness to be seen as a political tool stems from its own history. In 1976, a Senate investigation led by Frank Church, Democrat of Idaho, exposed that, for decades, the F.B.I. and other intelligence agencies had conducted controversial covert activities against not only foreign leaders but also American citizens. “Too many people have been spied upon by too many government agencies and too much information was collected,” the committee wrote, in its final report. Specifically, the committee found that “the government has often undertaken the secret surveillance of citizens based on their political beliefs, even when those beliefs presented no risk of violence or illegal acts on behalf of a hostile foreign power.” From the nineteen-fifties through the seventies, under the directorship of J. Edgar Hoover, the F.B.I. tapped Americans’ phones, broke into their homes, and opened a hundred and thirty thousand private letters in order to obtain personal information that it used to discredit individuals and groups. Over the course of fifty years, F.B.I. agents compiled a 2,076-page investigative file on the U.S. Supreme Court, to monitor Communist infiltration there, using Court employees as informants. At one point, the Bureau created a list of twenty-six thousand Americans to be rounded up in case of “national emergency.” It singled out African-American groups for infiltration, wiretapping, and intimidation, and set out to “destroy” Martin Luther King, Jr., during the last five years of his life.

The Church committee also found that every President from Franklin D. Roosevelt to Richard Nixon had improperly used the F.B.I. to collect information on political opponents. Before the United States entered the Second World War, F.D.R. asked the Bureau to create files on Americans who had sent telegrams to the White House opposing his “national defense” policy and supporting Charles Lindbergh’s isolationist stance. Dwight Eisenhower received reports on “purely political and social contacts” between foreign officials and Eleanor Roosevelt and Supreme Court Justice William O. Douglas. John F. Kennedy had the F.B.I. wiretap a congressional staffer, three executive officials, a Washington lobbyist, and a local law firm. Lyndon Johnson asked the Bureau to conduct background checks on senators who criticized him, and on members of the staff of his 1964 election opponent, Barry Goldwater. Most famously, Nixon set up a wiretap program that collected “purely political or personal information that was unrelated to national security, including information about a Supreme Court Justice.”

In an effort to restore public confidence in government, the Church committee issued ninety-six recommendations designed to create greater legislative- and judicial-branch oversight of the F.B.I., C.I.A, and other intelligence agencies. Citing the abuses of Hoover’s forty-eight-year tenure—including reports that he had blackmailed Presidents and members of Congress—directors were barred from serving more than a single ten-year term. F.B.I. and C.I.A. officials were ordered to provide neutral, non-politicized intelligence and analysis to policymakers, and instructed to not advocate for specific policies. Since then, F.B.I. directors have strived to be seen as nonpartisan. Suspicions remained, on the right and the left, but the reforms restored confidence among many Americans that, for the most part, the Bureau was no longer meddling in politics. Conversely, the spectre of another Watergate has generally precluded Presidents, Republican and Democratic alike, from overtly using the Bureau for political purposes—until now.

Since taking office, Trump has called the F.B.I. “a disgrace” and portrayed himself as the victim of a “deep state” conspiracy, led by the Bureau, that is trying to force him from office while protecting Hillary Clinton. The attacks are widely seen as an effort by Trump to persuade his supporters to disregard the findings of the investigation led by the special counsel, Robert Mueller. In the process, the former official said, Trump is rekindling mistrust in the F.B.I. “The Bureau did some really bad things, and it has taken decades to rebuild the trust of the American people,” the former official said. “Now you have manufactured allegations against the Bureau that are destroying that trust. Will it take another generation or two to rebuild that trust?”

In the final week of Kavanaugh’s confirmation battle, three different types of investigations by the Bureau were conflated. The most thorough and common investigations are criminal and national-security probes, which the Bureau itself controls, and in which agents can request subpoenas and search warrants, and interview as many people as they please. A second, less common type of review is a background investigation of a potential appointee to a government position, requested by his or her hiring agency, in which agents interview the candidate, review government and public records about his or her activities, and interview the person’s friends, associates, and neighbors. A supplemental background investigation is the smallest in scope and controlled by the agency ordering it—in Kavanaugh’s case, the White House.

Democrats dismissed the supplemental background investigation as a “sham” and said that Republicans exaggerated its thoroughness to ease Kavanaugh’s confirmation. (Senator Susan Collins, of Maine, a key Republican swing vote, said that the investigation “appears to be a very thorough.”) The former F.B.I. official told me, “The Administration knows that most Americans won’t distinguish between a criminal investigation and an F.B.I. background investigation.” So, “whatever result comes out of this will appear to the F.B.I. signing off on it.”