Ex-FBI chief: Mueller testimony must ‘wake up’ Republicans to the danger in the White House
Former FBI Deputy Director Andrew McCabe (Screen cap).

Former acting FBI Director Andrew McCabe appeared on MSNBC's "Deadline with Nicolle Wallace" to detail what he thinks will happen in the closed-door testimony from former special counsel Robert Mueller.

In a Wednesday interview, McCabe said he hopes that Mueller will "wake up" Republicans who seem uninterested  in acting to protect the United States from electoral intrusion from Russia.

Because President Donald Trump denied Russian meddling for so long, Congress never did anything meaningful to protect Americans from further intrusion or additional interference from other countries. McCabe said that Mueller would be able to convey details behind closed doors to reinforce why it is essential someone act in American interest in absence of the president.

"I think you only have to look back as far as the very limited nine-minute statement Director Mueller gave just a few weeks ago, [and how it] completely changed the conversation around the report, around the investigative findings and the impact that the report has had on people in Congress and I think on the general public," McCabe told Wallace.

"So if you extrapolate out from that very brief statement, to think about Director Mueller sitting behind the witness stand answering questions from both sides, I do agree with your panelist he will likely stay within the four corners of his report but there's incredible ground to cover there, and I think there are revelations that many, many people have not heard before, have not read in the report," McCabe continued. "So I think you can't underestimate the significance of the director's upcoming testimony."

Wallace agreed, noting that people must hear from Mueller about what his team uncovered and how those concerns are being addressed at the White House and in Congress.

McCabe noted that the report cites over 140 different interactions between people associated with the Trump campaign and Russians or individuals associated with Russian intelligence.

"That is a feast for counterintelligence investigators to feed upon, to investigate, to peel back the cover on for years and years to come," McCabe said.

He went on to say that many counterintelligence professionals must grapple with whether or not to share the information with Congress and in public. In Muller's case, McCabe said that he's "obligated to share" his work with Congress to keep intelligence communities abreast of the developments, problems and failures.

"There are many things Mueller did that he didn't want to do," McCabe said. "But he did it because his country needed him. He is an American Hero."

Trump and Fox News have already gone on the attack against Mueller.

Watch the full interview below: