The White House ethics lawyer under President George W. Bush said Thursday that Congress needed to make it clear to President Trump that firing special counsel Robert Mueller would mean his impeachment.

In a Twitter post Thursday evening, Richard Painter, who also serves as vice chairman of Citizens for Responsibility and Ethics in Washington, said that if Trump fires Mueller, it should be "bye-bye" Trump or "bye-bye" Congress.

"Congress must make it very clear: Bye-bye Mueller, bye-bye Trump. Otherwise bye-bye Congress 2018. Americans are fed up," Painter tweeted Thursday.

Congress must make it very clear: Bye-bye Mueller, bye-bye Trump.

Otherwise bye-bye Congress 2018. Americans are fed up! — Richard W. Painter (@RWPUSA) July 20, 2017

Painter, who served as Bush's chief ethics lawyer from 2005 to 2007, appeared to be referring to President Trump's remarks warning Mueller on Wednesday against investigating his family's finances beyond the Russia probe in an interview with The New York Times.

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“I think that’s a violation. Look, this is about Russia,” Trump told the Times on Wednesday.

On Thursday, Bloomberg reported that Mueller was investigating Trump's personal finances and business transactions as part of the probe. In a statement, Trump's lawyer called the move "well beyond" Mueller's mandate as special counsel.

"Those transactions are in my view well beyond the mandate of the special counsel," Trump’s lawyer John Dowd said in a statement to Bloomberg.

Others besides Painter warned Trump not to fire Mueller on Thursday. Sen. Marco Rubio Marco Antonio RubioSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Florida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll MORE (R-Fla.) said firing the former FBI director would be a "mistake."

“It would be a mistake to fire Bob Mueller," Rubio told reporters Thursday.