Several Democrats in Congress warned President Trump on Friday that he will face consequences if he fires 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,” Rep. Ted Lieu (D-CA) told MSNBC Friday. “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.”

Rep. Adam Schiff (D-CA) echoed Lieu’s sentiments, saying that Congress would come together to make sure they overrule Trump’s authority on the matter.

“Congress will not allow the president to so egregiously overstep his authority,” Schiff said in a statement.

“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 added.

Trump claimed on Twitter that he was “being investigated” for his decision to fire former FBI Director James Comey, insinuating that “the man who told [him] to fire the FBI Director” is also the one investigating him, referencing the deputy attorney general. He concluded the tweet by saying that the investigation is a “witch hunt” against him:

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

In his Tuesday testimony before the Senate, Rosenstein said he would only fire Mueller under “lawful and appropriate orders” to prove Mueller’s firing is for a “good cause.”

Sen. Dianne Feinstein (D-CA) saw Trump’s tweet as evidence that the president would fire the deputy attorney general.

“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.