Acting FBI Director Andrew McCabe is under mounting scrutiny and increasing calls for him to step aside amid allegations of politicized leadership, conflicts of interest and significant investigative missteps at the nation’s top law enforcement agency.

McCabe’s close alliance with Trump nemesis and former director James Comey, the well-chronicled fact his wife took a huge campaign donation from Virginia Gov. Terry McAuliffe and a general suspicion of the Obama intelligence community brass are all leading to pressure on FBI Director-Nominee Christopher Wray to not keep him around, according to former FBI insiders.

The latest challenge is coming from a former FBI agent who told Fox News that McCabe has created an overly politicized environment at the bureau, and her career suffered because of it.

“There is no way McCabe can survive. I’d be surprised." — Former FBI Assistant Director James Kallstrom

“McCabe is vicious to anyone who either stands up to him or is a threat to his ‘power’ and [he] is a screamer,” said former Supervisory Special Agent Robyn Gritz, who lost her job after 16 years with the FBI investigating some of the most high profile terrorist incidents in recent history, after getting tangled up with her superiors, who pushed her out and pulled her security clearance.

One of those superiors was McCabe.

“He saw me as a real threat to his climb because I knew my stuff and had been close to John Pistole, the prior deputy director. Andy resented that big time,” Gritz told Fox News.

According to Circa News, Gritz's sexual discrimination and retaliation complaint is one of three such administrative inquiries faced by McCabe.

Perhaps more damning, former FBI Assistant Director James Kallstrom said McCabe, who President Trump interviewed for the top job after firing Comey, may not have the bureau's rank and file behind him.

“McCabe is where he’s at because he’s very good at relating up the chain of command, but not down the chain of command, and that’s very typical of bureaucracies,” Kallstrom said. “McCabe told Congress FBI morale is high. I have not heard one person from the bureau tell me the FBI is happy because the investigative unit was thrown in front of the bus.”

Kallstrom was referring to McCabe’s reported role in several controversial probes during the 2016 election. According to the Wall Street Journal, it was McCabe who told lower-level FBI investigators to “stand down” in their inquiry into whether illegal influence-peddling or financial crimes were being committed at the Clinton Foundation. Meanwhile, McCabe did not recuse himself from the investigation into presidential candidate Hillary Clinton’s emails, despite an apparent conflict of interest involving his wife.

Jill McCabe’s losing campaign for a Virginia state Senate seat reportedly received $700,000 from Clinton allies at the same time that McCabe was second-in-command at the FBI during the investigation into her use of a personal email server for State Department business and alleged mishandling of classified information.

Comey declined to bring charges after determining that Clinton “lacked criminal intent.” Comey’s handling of the case was sharply criticized by Deputy Attorney General Rod Rosenstein in the memo outlining the rationale for firing Comey earlier this year. Kallstrom believes McCabe should have recused himself from any decisions involving the Clinton probe.

“I’ve talked to numerous agents that have some knowledge of what’s going on inside the FBI,” said Kallstrom. "The appearance of conflict of interest is substantial, and you can’t have a high position in the bureau and have even the apparent conflict of interest.”

Sen. Charles Grassley, R-Iowa, believes McCabe also has a conflict of interest in the ongoing probe into alleged Trump collusion with Russia in the 2016 election. The probe already cost retired U.S. Army Lt. Gen. Michael Flynn his job as Trump's national security adviser.

But even before the FBI eyed Flynn, he and McCabe had a history together, at the center of which was Gritz.

“McCabe wrote false and nasty comments on numerous documents about me when he had not one bit of proof of any lack of performance,” Gritz told Fox News, “I was always rated in the top two ratings.”

Flynn spoke out in her defense at the time, since the two had worked together when he led the Defense Intelligence Agency.

“I thought she was a real pro,” Flynn told NPR. Flynn was one of several top generals, including Stanley McChrystal and Keith Alexander, who wrote commendations for her counter-terrorism work, said Gritz.

In a June 29 letter addressed to Rosenstein, Grassley, who chairs the Senate Judiciary Committee, asked why McCabe did not recuse himself from the probe into Flynn’s connections to Russia. Justice Department protocol advises employees to recuse themselves from investigations if their involvement creates even the appearance of a conflict of interest.

With Flynn a potential witness for Gritz, Grassley wondered in his letter if McCabe “had any retaliatory motive against Flynn for being an adverse witness to him in a pending proceeding.”

The FBI, DOJ and the government’s Office of Special Counsel would not comment for this report.

With all of the various controversies swirling and President Trump under pressure to "drain the swamp" and fight back against the so-called "deep state," Kallstrom is not betting on McCabe lasting much longer at the bureau. Wray, who was formally advanced by the White House this week, is expected to be confirmed when the Senate takes up his nomination.

“There is no way McCabe can survive," Kallstrom said. "I’d be surprised."