What is so unusual about the current moment, say current and former law enforcement officials, is the source of the attacks.
The bureau is under fire not from those on the left but rather conservatives who have long been the agency's biggest supporters, as well as the president who handpicked the FBI's leader.
Republican critics charge that the birth of the investigation into possible coordination between the Trump campaign and agents of the Russian government was fatally infected by the political bias of senior FBI officials — and President Trump tweeted Saturday that the release of a memo on the issue "totally vindicates 'Trump.' "
Bureau officials say the accusations in the document produced by House Republicans are inaccurate and — more damaging in the long term — corrode the agency's ability to remain independent and do its job.
One law enforcement official summed it up bluntly: "There's a lot of anger. The irony is it's a conservative-leaning organization, and it's being trashed by conservatives. At first it was just perplexing. Now there's anger, because it's not going away."
On Friday, FBI Director Christopher A. Wray sent a video message to those he leads, urging them to "keep calm and tackle hard."
"You've all been through a lot in these past nine months, and I know that's been unsettling, to say the least. And the past few days haven't done much to calm those waters," Wray said. "So I want to make sure that you know where I stand, and what I want us to do."
Most FBI agents see their mission as fundamentally nonpolitical — ferreting out wrongdoing, even when that occurs inside political campaigns or government.
For decades, the FBI has been trusted to investigate corruption inside the government, even at the highest levels, including the White House. In the 1970s, the FBI's probe of the Watergate break-in led to the resignation of President Nixon. In the late 1990s, President Bill Clinton came to detest then-director Louis Freeh, but their distrust did not lead to withering public attacks from the president himself.
After the Sept. 11, 2001, attacks, the agency was retooled to focus primarily on preventing terrorism, and public confidence in its work grew. In the past two years, however, the probe of Hillary Clinton's use of a private email server while she was secretary of state and a separate Russia investigation are testing whether the FBI can maintain the trust of Congress, the courts and the country.
Wray's vision for leading the agency out of its current predicament is a return to the type of low-profile management favored by former FBI director Robert S. Mueller III, according to several people who have spoken to him about the current challenges.
Wray's predecessor, James B. Comey, was fired by Trump in May amid the ratcheting tensions of a criminal probe into the president's former national security adviser, Michael Flynn. At the time, Trump called Comey a "showboat" and a "grandstander."
It makes sense, then, that his successor would want to keep his head down.
Wray's defenders say there is a more strategic reason for the new director's approach — by relying on long-standing law enforcement policies and procedures, he believes the FBI can navigate through the current political storms and get back to a position of widespread trust across the political spectrum, according to people familiar with his thinking.
"Following established process is important," one person said. "Process can protect us."
That approach, though, is a subtle rejection of some of Comey's most controversial decisions. Comey famously held a news conference in July 2016 to announce he would not recommend any criminal charges in the probe of Clinton's use of a private email server when she was secretary of state. Then in October of that year, less than two weeks before the presidential election, he sent a letter to Congress informing them that the FBI was investigating new emails in the case.
Comey's firing shocked the FBI's workforce. In the aftermath, many employees posted pictures of him at their desks or other workspaces.
"In some offices, you'd go in and it was just, 'Comey, Comey, Comey' everywhere," said one law enforcement official. "There's still a lot of that, but not as much."
The public attacks from the president have diminished morale inside the FBI, according to current and former officials. Among themselves, senior officials and rank and file frequently debate the best way forward. Several law enforcement officials said they agreed with Wray's low-key approach, as a means of what one called "getting back to Mueller's FBI."
That is a sentiment not without irony because Mueller is now the special counsel leading the Russia investigation so despised by the president and his allies. On Saturday in his tweet, Trump said the "Russia Witch Hunt goes on and on . . . This is an American disgrace!"
Others express doubts about emulating Mueller's detached approach, worried that Wray's calculation not to publicly spar with the president may lead to a gradual erosion of the bureau's reputation and clout. One law enforcement official expressed worry that they might not be able to return to an earlier era because, as he put it, "this Pandora's box of politics has been opened, and we may never get rid of it."
A HuffPost/YouGov poll last month found that 51 percent of the public say they have a fair amount of trust in the FBI — down 12 points from 2015. Most of that drop was driven by Republicans and independents, the poll found.
The so-called #ReleaseTheMemo campaign — a GOP effort to make public the four-page document produced by House Intelligence Committee Chairman Devin Nunes (R-Calif.) alleging surveillance abuses by the FBI — is just the latest salvo in an escalating war on the credibility of federal law enforcement. On Friday, over Wray's objection, Trump authorized the release of the Nunes memo and declared, "A lot of people should be ashamed of themselves and much worse than that.''
The document — which Democrats said lacked appropriate context and seemed to be a pretext for conservatives to discredit the investigation into Trump — alleged the FBI misled the Foreign Intelligence Surveillance Court in obtaining a secret warrant to monitor former Trump campaign adviser Carter Page.
That was because, Republicans alleged, the bureau did not tell the court that they were relying in part on information they had received from an ex-British spy who was working for an opposition research firm hired by the Clinton campaign and the Democratic National Committee. Officials familiar with the matter, though, said the court that approved the warrant was aware some information in the request was funded by a political entity, even if that entity was not specifically named.
"That's it?" Comey tweeted after the memo was released Friday. "Dishonest and misleading memo wrecked the House intel committee, destroyed trust with Intelligence Community, damaged relationship with FISA court, and inexcusably exposed classified investigation of an American citizen. For what? DOJ & FBI must keep doing their jobs."
Trump's attacks on the Justice Department and the bureau are not new. He has called his own attorney general "beleaguered" and claimed the bureau's reputation was "in tatters." But in recent weeks, his claims have been magnified by Republicans on Capitol Hill and buttressed by the release of materials that call into question the actions of some agents.
Late last month, Sen. Ron Johnson (R-Wis.) said on Fox News there was "evidence of corruption — more than bias but corruption — at the highest levels of the FBI," and pointed to texts between two key officials who were once assigned to both the Clinton and Trump probes suggesting a "secret society" at the FBI. Those messages about a "secret society" are now widely seen to be a joke, but that has not diminished Republicans' fervor about what they see as malfeasance in federal law enforcement.
Next came days of wrangling over whether the memo should be released, with the Justice Department and Republicans trading barbs over whether the document might harm national security and if it was accurate. Trump ultimately sided with Hill Republicans, even over the advice of his own FBI director.
The Justice Department typically has a unique role in an administration: While it seeks to implement the president's policy goals as a part of the executive branch, it conducts criminal investigations independently and without regard to the will of the chief executive. Trump has defied that norm. He asked Comey for a vow of loyalty, then inquired with Andrew McCabe, who replaced Comey after Trump fired him, for whom he voted.
The president's approach has scrambled old alliances and created some odd new ones.
Privacy advocates — whose mission often centers on trying to rein in what they view as the FBI's overbroad and unchecked surveillance powers — have found themselves defending the agency in the current fight, saying the GOP's claims of privacy abuses lack a factual foundation.
"For a long time we've had a concern about the process for obtaining surveillance, a warrant to surveil an American citizen, and abuses in that process," said Christopher Anders, deputy director of the American Civil Liberties Union's Washington Legislative Office. "And with Congressman Nunes's memo raising concerns that there were abuses in that process, of course that's something that would concern us. The memo itself, though, doesn't prove the case. It doesn't have the kind of evidence in it that you would need to see to say that there was an abuse of that authority."
Ron Hosko, a former FBI assistant director, said some of the president's behavior toward the Justice Department and the FBI might do lasting damage. While the president might now feel he wants the bureau under his firm control, Hosko said, he might regret that if a like-minded president took office and ordered investigations of Trump or his family.
"The battle is incredible, and who's riding to the defense of the FBI? The Democrats," said Hosko. "It just makes no sense."
Current and former law enforcement officials expect the struggle for control of the FBI to intensify.
"Republicans feel the White House is under siege and have suspicions that the FBI was not playing fair,'' said one former senior Justice Department official. "Republicans think this is just part of the war they are fighting."