Rep. Adam Schiff (D-CA) responded to President Donald Trump’s bizarre Friday statement that appeared to confirm he’s the subject of an obstructive of justice investigation, urging Congress to take precautions against any presidential interference.

“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 wrote Friday. “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 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 continued.

Trump wrote on Twitter Friday that “I am being investigated for firing the FBI Director.” He has posted frequently this week about his displeasure with the federal investigation into Russian interference in the 2016 election.

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

Speaking to reporters in an off-camera briefing Thursday, deputy White House press secretary Sarah Huckabee Sanders said that Trump “has the right to” fire Mueller as special counsel but “has no intention to do so.”

Schiff on Friday urged his colleagues to “defend our system of checks and balances by passing an independent counsel law that empowers an independent prosecutor to take over the Russia investigation and anything that arises from it.”

“Such a law should allow for the reappointment of Bob Mueller, someone who has served Presidents of both parties and whom Democrats and Republicans have come to admire,” he wrote. “We cannot allow the President to choose who will conduct this investigation or to interfere with its progress in any way.”

Sen. Dianne Feinstein (D-CA) also came out strongly against Trump firing either Rosenstein or Mueller Friday, writing that “[t]he 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.