Former FBI Deputy Director Andrew McCabe said impeachment proceedings against President Trump should begin "immediately."

He was asked during an appearance Thursday evening on CNN whether special counsel Robert Mueller's findings and his understanding of Trump's actions warranted an impeachment inquiry.

"Absolutely," he told host Chris Cuomo.

McCabe acknowledged House Speaker Nancy Pelosi's resistance against pursuing impeachment, fearing backlash from the electorate.

But McCabe insisted that impeachment proceedings "could provide important, essential testimony to Congress that can only be done in the scope of an impeachment inquiry."

McCabe said action "should be taken immediately" and added that "whether or not that results in articles of impeachment and trial in the Senate and all of those sorts of things is beside the point."

Mueller completed his 22-month investigation into Russia interference in the 2016 election in March. His report, released by the Justice Department with redactions in April, shows Mueller's team was unable to criminal conspiracy between the Trump campaign and the Kremlin. Mueller outlined 10 scenarios of possible obstruction in his report but declined to make a determination about whether the president obstructed justice.

Although Trump says he has been vindicated, Democrats argue Mueller's refusal to clear Trump on obstruction provides them a road map to continue to investigate and possibly seek impeachment. Attorney General William Barr said he and former Deputy Attorney General Rod Rosenstein determined there was not sufficient evidence to establish a crime had occurred.

Trump stirred controversy this week when he told ABC News he would be willing to accept opposition research from a foreign government in the future. McCabe said that is "not acceptable."

McCabe's endorsement of impeachment is notably a step further than his former boss, ex-FBI Director James Comey, has gone. Comey warned in March that the country "would see this as a coup" and has pushed for pushing Trump out of office in the 2020 election.

McCabe was fired from the FBI on March 16, 2018, after the Justice Department's Office of the Inspector General determined he misled investigators about the role he had in leaking information to the Wall Street Journal in October 2016 about the investigation into the Clinton Foundation. McCabe argued that his firing was an attempt to discredit the FBI and Mueller's investigation.

In April 2018, it was revealed that the Justice Department inspector general had referred its findings to the U.S. attorney’s office in Washington for possible criminal charges, and his lawyer confirmed in February that McCabe was still under investigation.