Key US Senator: Trump Firing of Mueller Could Provoke 'Constitutional Crisis'
WATCH: Virginia's Warner on Potential Constitutional Crisis
Speaking on the Senate floor, Virginia Senator Mark Warner denounced attacks on Mueller's impartiality and said the special counsel's investigation of ties between Trump's presidential campaign and Russia must be "able to go on unimpeded."
Russia denies that it meddled in the 2016 U.S. presidential election, and Trump has denied any collusion.
While Trump's political allies have increased their criticism of Mueller, the president said Sunday that he was not considering firing him.
Republican lawmakers have seized on anti-Trump texts by a Federal Bureau of Investigation agent who was involved in the Russia investigation as evidence of bias in Mueller's team.
Mueller removed the agent from his team after the texts came to light.
Republicans on several House of Representatives committees also have announced their own probes into long-standing political grievances, including the FBI's handling of Hillary Clinton's use of a private email server when she was secretary of state.
"Over the last several weeks, a growing chorus of irresponsible voices have called for President Trump to shut down special counsel Mueller's investigation," said Warner, who is vice chairman of the Republican-controlled Senate Intelligence Committee.
"Firing Mr. Mueller or any other of the top brass involved in this investigation would not only call into question this administration's commitment to the truth, but also to our most basic concept of rule of law," Warner said. "It also has the potential to provoke a constitutional crisis."
"In the United States of America, no one, no one is above the law, not even the president," the senator said.
WATCH: Warner on Consequences of Mueller Removal
"Congress must make clear to the president that firing the special counsel or interfering with his investigation by issuing pardons of essential witnesses is unacceptable and would have immediate and significant consequences."