The Federal Bureau of Investigation, once America's storied crime fighting agency, is under fire for an increasing leftward politicization blamed on recent liberal directors and a bureaucracy operating with nearly unchecked power.

Once a bastion of conservative anti-communism under long-time director J. Edgar Hoover, the FBI has become one of the more liberal political agencies of government, and some critics say appears increasingly to operate outside normal constitutional controls.

The shift is the result of a bureaucratic culture that emerged in the 1990s and was fueled by its two most recent former directors, James Comey and Robert Mueller, who ran the agency for the past 16 years. Mueller headed the FBI from 2001 to 2013, when Comey took over and served until he was fired by Trump in May.

Both former directors currently are at the center of a fierce political debate over the FBI's competency and integrity.

"People are finally tumbling to the realization that this [FBI] has become a proto-KGB," said a former senior intelligence official with extensive experience in counterintelligence. "We're in a constitutional crisis. These guys are playing out a silent coup against an elected official."

President Trump castigated the FBI this week in unusually harsh tweets and comments.

Commenting on disclosures that the Justice Department's inspector general launched an investigation of political bias by senior FBI Agent Peter Strzok working for Mueller's Russian election meddling probe, Trump compared the FBI's lenient approach to Hillary Clinton's misuse of a private email server while secretary of state with the recent case of former Trump National Security Adviser Michael Flynn who pleaded guilty to lying to the FBI about post-election contacts with Russia.

"Tainted (no, very dishonest?) FBI ‘agent’s role in Clinton probe under review.' Led Clinton Email probe. @foxandfriends Clinton money going to wife of another FBI agent in charge," Trump tweeted on Sunday.

"After years of Comey, with the phony and dishonest Clinton investigation (and more), running the FBI, its reputation is in Tatters – worst in History! But fear not, we will bring it back to greatness," the president declared.

On Tuesday, Mueller appeared to counter the comments by leaking word he has issued subpoenas for bank records at Deutche Bank related to Trump and members of his family.

The leak produced a spate of news stories under the ongoing liberal narrative of the past year of alleged Russian collusion with the Trump campaign, a narrative lacking hard facts.

The problem of the FBI, according to national security strategist Angelo Codevilla, is more the result of careerism and an out of control bureaucracy than liberal politicization of the ostensibly nonpartisan FBI, the nation's most powerful law enforcement agency and main domestic counterspying and counterterrorism agency.

"I’m afraid that the explanation is all too simple: Bureaucrats—employees of large organizations—figure out on which side their bread is going to be buttered," Codevilla said. "They learn to think, feel, and do what advances their careers."

Under President Barack Obama, the FBI suffered a string of failures that critics blame on the FBI being pressured by liberal, politically correct policies that emphasized diversity and multiculturalism of its workforce over competence and results.

The problem is evident whenever a U.S.-based terror attack or other major crime takes place and the FBI, seemingly ever on the lookout for ways to protect its reputation, puts out word to pro-FBI news reporters that the problem is less serious than it is.

That was the case shortly after several major Islamic terror attacks in the United States when Bureau officials initially put out word the attacks had no link to terrorism.

Similarly, when North Korea conducted a major cyber attack against Sony Pictures Entertainment in 2014, the FBI agent heading the probe at first said there was no foreign involvement in the hack.

In another case last June, after an anti-Trump gunman—and Sen. Bernie Sanders (I., Vt.) supporter—shot a congressman and four other people in Alexandria, the FBI sought to minimize the politics of the incident. The agent running the investigation, Tim Slater, told reporters the shooting was "spontaneous," despite evidence the shooter had a list of targeted members of Congress.

John Guandolo, a former FBI counterterrorism agent, has criticized the FBI for caving in to pressure from Muslim groups in watering down its training of agents by limiting references to Islam and jihad, or holy war.

"I am not aware of any time in the FBI's history when FBI leadership was so incapable of performing their duties as they are today," Guandolo said.

"The FBI's inability or lack of desire to aggressively pursue obvious major threats to the republic—the Marxist and Islamic movements for instance—is stunning and frightening."

Guandolo said that instead the FBI is working with "our Islamic enemy."

"In fact, all three of the Muslim organizations listed on the FBI's website as ‘Outreach Partners' are Muslim Brotherhood organizations," he said.

Additionally, liberal left or Marxist inclinations appear to motivate some of the FBI's key leaders.

Guandolo said FBI Deputy Director Andrew McCabe was promoted by Comey despite internal leadership reviews that questioned his fitness.

Congressional Republicans are investigating whether McCabe should have recused himself from the Clinton email probe.

McCabe's wife, a Democrat, received payments of some $700,000 from a political action committee affiliated with Virginia Gov. Terry McAuliffe, a close ally of Clinton, during a failed bid to run for the state senate.

The president's online criticism of the FBI was followed by comments he made Monday calling the FBI's treatment of Flynn "very unfair" compared to how the Bureau treated Clinton during last year's election-year investigation into the misuse of her private email server.

"I feel badly for Gen. Flynn. I feel very badly. He’s led a very strong life," Trump told reporters outside the White House. "I will say this, Hillary Clinton lied many times to the FBI and nothing happened to her. Flynn lied, and they destroyed his life. I think it’s a shame."

The president referred to the July 2, 2016, FBI interview of Clinton regarding her use of a private email server used while she was secretary of state to send some highly classified information and the deletion of emails after published reports of the private server revealed the existence of it.

Clinton, according to the FBI summary of the interview, asserted she did not recall being given a security briefing on handling information held in Special Access Programs (SAP), the government's most sensitive secrets. Some SAP information on drone strike targeting was found on her private email server.

Days after the FBI interview, Comey issued his now famous public statement recommending against prosecuting Clinton for mishandling classified information, despite evidence the mere presence of the secret information is a crime.

Comey also would later disclose that under political pressure for Obama Attorney General Loretta Lynch he agreed not to refer to the email scandal as an investigation and instead call it a "matter."

Comey also granted immunity from prosecution for two key witnesses, Clinton aides Cheryl Mills and Heather Samuelson. The immunity prevented the FBI from conducting searches for evidence. The immunity deal also required the FBI to destroy the two aides' laptops after they were searched, a step that potentially eliminated evidence of a crime.

In October, Sens. Chuck Grassley (R., Iowa) and Lindsey Graham (R., S.C.) revealed that Comey had decided in May 2016—months before the FBI probe of Clinton was completed—that he was planning to issue a statement exonerating Clinton.

"Conclusion first, fact-gathering second—that's no way to run an investigation," the senators said in a letter to FBI Director Christopher Wray in August. "The FBI should be held to a higher standard than that, especially in a matter of such great public interest and controversy."

An FBI source said Comey's politically charged handling of the Clinton email probe upset many of the FBI's agents who saw it as a disheartening indication of political bias in favor of Clinton.

Trump fired Comey in May prompting the Justice Department to create the special counsel investigation headed by Mueller, a long-time Comey associate.

The more recent disclosures that one of Mueller's investigators, Strzok, is under investigation for anti-Trump bias is now raising new questions about the integrity of the special counsel probe and whether it too has reached a pre-determined outcome against the president.

The FBI also is under fire from Congress for refusing to provide documents to congressional investigators looking into the Democrat-funded private intelligence dossier at the center of Republicans' investigation into the potential misuse of security agencies for political ends.

The Bureau has so far refused to provide the House Intelligence Committee with details on how it pursued salacious allegations regarding Trump and the Russians contained in the dossier produced by former British intelligence officer Christopher Steele.

Rep. Devin Nunes (R., Calif.), chairman of the House Permanent Select Committee on Intelligence, said this week he is drafting a contempt of Congress resolution against Wray, the FBI chief, and Deputy Attorney General Rod Rosenstein for failing to disclose to Congress earlier Strzok's political bias against Trump.

Nunes revealed Strzok was involved in the Clinton email probe in addition to Mueller's election meddling probe and that hiding those facts from Congress was "a willful attempt to thwart Congress’ constitutional oversight responsibility."

"This is part of a months-long pattern by the DOJ and FBI of stonewalling and obstructing this committee’s oversight work, particularly oversight of their use of the Steele dossier," Nunes said. "At this point, these agencies should be investigating themselves."

Security experts said it is likely that Strzok, the senior FBI counterintelligence official who specializes in Russian spying, has been the driving force behind the mainly Democratic political narrative that Russia stole the 2016 election from Clinton and gave it to Trump.

Congress wants to question him about what role the discredited Steele dossier played in the FBI's Russian election meddling investigation.

One irony of the FBI's zealousness on the Russian election influence probe is that for many years during the 1980s, the FBI refused to acknowledge that Moscow at the time was engaged in similar sophisticated disinformation and so-called "active measures" operations against the United States.

Under the Reagan administration, the FBI was forced to investigate and take steps to counter Moscow's intelligence-driven influence operations.

Now it seems the FBI is convinced, despite the lack of evidence, there was a Russian conspiracy to elect Trump and it is searching for a way to prove its theory.

Observers say a major problem for the FBI today is a lack constitutional oversight and controls. Bureau leaders have created the myth that the White House or any agency cannot have any control over the FBI.

That is not true. While it would be illegal for the White House to interfere or corrupt FBI investigations, the Constitution makes clear the FBI, as an executive branch agency, is ultimately responsible to the president.

Under the Comey-Mueller bureaucracy, however, the FBI seems to regard itself as a power center answerable to no one, critics say.

According to FBI sources, FBI agents and other personnel have been told unequivocally that they are not to have any dealings with the White House, and that doing so risks career-ending measures.

As for Congress, the FBI for years also has stonewalled overseers under both Comey and Mueller.

Even routine requests for FBI documents and information have been rejected or ignored, and congressional overseers have not taken action to force the FBI to comply.

The lack of congressional oversight and administration controls have left the FBI with enormous power and little accountability.

The former intelligence official, who spoke on condition of anonymity over concerns about FBI retaliation, said the mindset of Comey, Mueller and others of their group is that they are going to punish Trump for his criticism of the FBI.

"Mueller, Comey, and Rosenstein are going to make Trump pay for having dissed the bureau," the former official said.

A spokesman for Mueller did not respond when asked if the special counsel probe has been tainted by Strzok's involvement.

"Immediately upon learning of the allegations, the special counsel’s office removed Peter Strzok from the investigation," the spokesman said.

An FBI spokesman defended the FBI's handling of the issue of Islamic threat training and said the Defense Department and not the FBI was the first to refer to the Fort Hood terror attack as workplace violence.

On Strozk, FBI spokesman Andrew Ames referred to the statement on the matter.

"The matter is an ongoing investigation by the Office of Inspector General, consistent with well-established processes designed to objectively, thoroughly and fairly determine the facts regarding potential wrongdoing," the statement said.

"The FBI has clearly defined policies and procedures regarding appropriate employee conduct, including communications," the statement added. "When the FBI first learned of the allegations, the employees involved were immediately reassigned, consistent with practices involving employee matters.

The FBI employees are held to "the highest standards of integrity, independence and professionalism, as the American public rightly expects."

Disclosure: The Washington Free Beacon was once a client of Fusion GPS, which produced the Steele dossier. That relationship ended in January 2017. For more information, see here."