Former independent counsel Ken Starr said special counsel Robert Mueller’s “whiny” letter to Attorney General William Barr regarding his summary of the Russia investigation was an “unforgivable sin.”

Starr, who headed the 1990s-era Whitewater investigation that prompted the impeachment of President Bill Clinton, blasted Mueller’s letter that argued Barr’s four-page summary of the Russia investigation “did not fully capture the context, nature, and substance” of the investigation.