Former independent counsel Ken Starr said there would be "hell to pay" politically for President TrumpDonald John TrumpAmash responds to 'Send her back' chants at Trump rally: 'This is how history's worst episodes begin' McConnell: Trump 'on to something' with attacks on Dem congresswomen Trump blasts 'corrupt' Puerto Rico's leaders amid political crisis MORE if he were to fire Attorney General Jeff SessionsJefferson (Jeff) Beauregard SessionsTrump's no racist — he's an equal opportunity offender Press: Acosta, latest to walk the plank The Hill's Morning Report — Trump retreats on census citizenship question MORE and the special counsel in charge of the Russia investigation, Robert MuellerRobert (Bob) Swan MuellerTop Republican considered Mueller subpoena to box in Democrats Kamala Harris says her Justice Dept would have 'no choice' but to prosecute Trump for obstruction Dem committees win new powers to investigate Trump MORE.

Asked by Bloomberg News anchor David Westin on Friday why Trump has not yet fired Sessions, who Westin notes serves "at the pleasure of the president," Starr predicted the president would face difficulties attempting to appoint Sessions's replacement.

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“I think that there would be hell to pay if the president fired Mueller or ordered the firing of Bob Mueller,” Starr said in the interview.

"Jeff Sessions I think is an honorable person who recused himself, so I think obviously the president has that prerogative, but it would be very hard to get a new attorney general confirmed," he continued. "We would have Rod RosensteinRod RosensteinFeds will not charge officer who killed Eric Garner The Hill's Morning Report — Trump retreats on census citizenship question Judiciary issues blitz of subpoenas for Kushner, Sessions, Trump associates MORE as the acting attorney general of the United States indefinitely."

Starr served on the 1998 Republican-led investigation of former President Clinton, who was eventually impeached by the House but not convicted by the Senate on charges of perjury and obstruction of justice.

Speculation has grown over whether Trump will fire Sessions or Mueller in recent weeks as Trump's tone on Twitter increasingly turned towards direct calls for the investigation to be ended by Sessions.

"Attorney General Jeff Sessions should stop this Rigged Witch Hunt right now, before it continues to stain our country any further," Trump tweeted in early August.

The president has also frequently attacked Mueller and the FBI investigators working with the special counsel's office, whom he frequently refers to as "angry Democrats."

"Bob Mueller is totally conflicted, and his 17 Angry Democrats that are doing his dirty work are a disgrace to USA!" he added in the same tweet.

Mueller's probe reached a milestone this week after prosecutors reached a plea agreement with Paul ManafortPaul John ManafortWebb: Questions for Robert Mueller Top Mueller prosecutor Zainab Ahmad joins law firm Gibson Dunn Russian oligarch's story could spell trouble for Team Mueller MORE, the president's former campaign chairman, sparing him from a second trial previously set to begin this month.