Former U.S. Solicitor General Kenneth Starr, who became a regular character in American politics as the independent counsel during President Bill Clinton’s impeachment proceedings, said President Donald Trump would be ill-advised to get rid of special counsel Robert Mueller.

Starr made the comments on Friday after Bloomberg’s David Westin asked him what the consequences would be if Trump were to fire Attorney General Jeff Sessions and get rid of Mueller.

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

On Friday morning, former Trump campaign chairman Paul Manafort pleaded guilty as part of a deal to fully cooperate with Mueller’s investigation into possible Russian interference in the 2016 presidential election.

In late August, Trump’s former lawyer Michael Cohen pleaded guilty to tax evasion, campaign finance violations and making false statements.

Trump on Saturday denied that his campaign colluded with Russia, and accused Democrats of trying to politicize Mueller’s investigation.

“Highly conflicted Bob Mueller & the 17 Angry Democrats are using this Phony issue to hurt us in the Midterms,” he tweeted. “No Collusion!”