Special counsel Robert Mueller committed an “unforgivable sin” by writing the “whiny” leaked letter criticizing the attorney general’s summary of the report on Russia, according to Ken Starr.

Mueller wrote in a letter that was eventually leaked to the press that Attorney General William Barr’s summary of his report “did not fully capture the context, nature, and substance of this office’s work and conclusions,” and that “there is now public confusion about critical aspects of the results of our investigation.”

Starr, the attorney whose investigation in the 1990’s led to former President Bill Clinton’s impeachment, told Fox News’ Martha MacCallum Monday night that Mueller’s “letter, that was then leaked on the very eve of Bill Barr’s testimony, was essentially, I believe, an unfair, whiny complaint.”

He added, “Here comes Bob Mueller with this letter which is then leaked. That is, to me, the unforgivable sin. He, Bob Mueller, badly injured this attorney general and the attorney general didn’t deserve that but, of course, that created its own huge firestorm including suggestions that the attorney general was totally mischaracterizing the report and so forth.”

Democrats on the House Judiciary Committee have requested that Mueller testify before them, but the special counsel has yet to agree. Barr testified before the Senate Judiciary Committee on Wednesday, but refused to attend a session with the House panel on Thursday.