Barr poses 'greatest threat' to our rule of law -Ayer

"Since taking office, he has worked to advance his life-long conviction that the President should hold virtually autocratic powers," Ayer said.

As Ayer spoke, committee member Louie Gohmert, a Republican, incessantly knocked on his desk in protest and was threatened with removal from the chambers.

U.S. Attorney General William Barr, under fire from Democrats for actions they view as politically motivated, will testify before the House of Representatives Judiciary Committee on July 28, a Justice Department spokeswoman said on Wednesday.