Two of the people believed to be at the center of a criminal investigation into the origins of the Trump-Russia investigation defended that investigation's legitimacy.

“There is nothing wrong with, especially a new attorney general, coming in at the conclusion of a tumultuous, high-profile, controversial case and asking questions about how that all began and what was the factual predication that led to the initiation of that investigation and how was it conducted. Those sorts of reviews take place all the time,” former FBI Deputy Director Andrew McCabe said a George Mason University event Wednesday at the National Press Club.

And former CIA Director John Brennan said investigators working with U.S. Attorney John Durham, who is leading the investigation, will "try to ensure that this is done appropriately."

"I would like to believe that any such review or investigation will be conducted in a professional, fair, and apolitical manner," Brennan said. "And John Durham has a very good reputation."

Earlier this year, Attorney General William Barr tapped Durham to look into the early stages of the Russia investigation through the appointment of special counsel Robert Mueller in 2017.

The investigation has since transitioned into a criminal investigation, but McCabe said that’s not unusual.

“It would be odd to expect Mr. Durham to conduct that sort of inquiry without having subpoena power and stuff like that," he said.

Both McCabe and Brennan, who has been highly critical of the Trump administration, said they had not been contacted by investigators, though McCabe expects to be.

"I look back on it and I feel good about what it is we did as an intelligence community, and I feel very confident and comfortable with what I did, so I have no qualms whatsoever about talking with investigators who are going to be looking at this in a fair and appropriate manner," Brennan said. "And so if I’m called, I will be happy to talk."

But both hinted at a fear Durham's investigation could be tainted by politics.

Durham's investigation could be justified "if the effort is to try to look back and to ensure that things were done appropriately," Brennan said, "as opposed to questioning the analytical assessment that was done and the judgments that came out of it."

"The problem with this is when you have a factual scenario, which I think we have now, that indicates that some folks, and possibly even the attorney general, are bringing a set of preconceived notions and biases to that investigation," McCabe said. "And if that’s the case, I don’t know that it is, but there’s certainly some indicators that it might be, or that the purpose of the investigation is not really to get to the bottom of what did we know and why did we make the decisions that we did, but it’s more to run out theories, political conspiracy theories, and things of that nature."

The former FBI leader said "that causes me great concern — not me personally — but of course about the state of the department and the intelligence community that’s currently under investigation."

Brennan also pointed a finger at Trump.

Whether there are political motivations, there's the appearance "at least in the minds of some that this is politically motivated, because of the continued insistence by Mr. Trump that this is all a grand hoax and the former leaders of the intelligence and law enforcement community were involved in this effort to subvert the candidacy and the electoral prospects of Mr. Trump, which is the furthest from the truth that it could be," he said.

Brennan also made a reference to the attorney general telling the Senate in April "spying did occur" during the Obama administration's Trump-Russia investigation.

"There were some things that Mr. Barr said in testimony that raised questions in my own mind about whether or not he was looking at this, again, through the prism of what an attorney general should be doing as opposed to looking at it from the standpoint of Mr. Trump’s lawyer," he said.

Michael Morell, who served as acting director of the CIA during the Obama administration, said he had “deep concerns” about Durham’s investigation, which he said could have a “chilling effect” on how analysts do their jobs.

“It’s highly inappropriate, because the Justice Department doesn’t have a lot of experience understanding the analytical process. They’re not experts. John Durham, as good as he is, as good of a prosecutor as he is, doesn’t understand how we do analysis, doesn’t understand how we evaluate information, doesn’t understand how we evaluate sources, doesn’t understand how we come to conclusions, doesn’t understand how we put confidence levels on them. He doesn’t understand that. He doesn’t do that for a living. He looks at issues and decides whether a crime has been committed,” Morell said.