Rep. Ted Lieu (D-Calif.) said Friday that Congress would come together and “begin impeachment proceedings” against President Trump if he fired special counsel Robert Mueller and Deputy Attorney General Rod Rosenstein.

“All Americans, regardless of party, agree on the fundamental principle that no one is above the law,” Lieu said on MSNBC. “And if President Trump were to fire Deputy Attorney General Rosenstein, and then [get] special counsel Mueller fired, I believe Congress would begin impeachment proceedings.”

Lieu’s comments come after Trump and his allies launched multiple attacks against Mueller's character and possible conflicts of interest in an attempt to discredit him and his investigation.

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For example, former Republican Speaker of the House Newt Gingrich accused Mueller of hiring Democratic political donors and called Mueller the “tip of the deep state spear," a conspiracy theory reference.

Trump himself used Twitter Friday to lash out at Rosenstein, saying he was “being investigated” for firing former FBI Director James Comey “by the man who told me to fire the FBI director,” seemingly referencing Rosenstein.

I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt — Donald J. Trump (@realDonaldTrump) June 16, 2017

Lieu isn’t the only House Democrat warning Trump of consequences for firing Mueller and Rosenstein. Rep. Adam Schiff Adam Bennett SchiffSchiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power Rubio on peaceful transfer of power: 'We will have a legitimate & fair election' MORE (D-Calif.), the top Democrat on the House Intelligence Committee, said Friday that Congress would “unite to stop [Trump] if he tried to fire the two men.

"It has become clear that President Trump believes that he has the power to fire anyone in government he chooses and for any reason, including special counsel Robert Mueller,” Schiff said in a statement. “That is not how the rule of law works, and Congress will not allow the president to so egregiously overstep his authority.”

"If President Trump were to try to replicate [former President Richard] Nixon’s Saturday Night Massacre by firing Deputy Attorney General Rod Rosenstein in addition to Mueller, Congress must unite to stop him – without respect to party, and for the sake of the nation," he said.

In the Senate, Sen. Dianne Feinstein Dianne Emiel FeinsteinTrump faces tricky choice on Supreme Court pick The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Abortion stirs GOP tensions in Supreme Court fight MORE (D-Calif.) issued a similar warning.

“The message the president is sending through his tweets is that he believes the rule of law doesn’t apply to him and that anyone who thinks otherwise will be fired. That’s undemocratic on its face and a blatant violation of the president’s oath of office," Feinstein said in a statement Friday.

“It’s becoming clear to me that the president has embarked on an effort to undermine anyone with the ability to bring any misdeeds to light, be that Congress, the media or the Justice Department. The Senate should not let that happen. We’re a nation of laws that apply equally to everyone, a lesson the president would be wise to learn,” she said.