Sen. Lindsey Graham warned Sunday “it would be the beginning of the end” of President’s Trump’s presidency if he fired special counsel Robert Mueller.

“As I said before, if he tried to do that, that would be the beginning of the end of his presidency,” Graham, R-S.C., said on CNN’s "State of the Union."

“Because we're a rule of law nation. When it comes to Mr. Mueller, he is following the evidence where it takes him and it's very important he be allowed to do his job, without interference. And there are many Republicans who share my view.”

Graham added Mueller is doing a “good job” and there is no legitimate cause to fire him.

“The only reason Mr. Mueller could ever be dismissed is for cause,” Graham said. “I see no cause when it comes to Mr. Mueller. I pledge to the American people, as a Republican, to make sure that Mr. Mueller can continue to do his job without any interference. He's doing a good job.”

In recent days. Trump has said Mueller’s investigation of Russia’s 2016 election interference “should never have been started” and accused the special counsel’s team of political bias.

Mueller is also probing whether the Trump campaign collaborated with Russia, and if the president has obstructed justice in trying to impede the probe.

Trump has escalated his attacks on the Russia probe after Attorney General Jeff Sessions fired Andrew McCabe as deputy director of the FBI.

McCabe was among the first FBI officials to be involved in investigating possible links between Russia and the Trump campaign.

Sessions said he fired McCabe on Friday night for failing to be transparent with the department’s internal watchdog about a conversation he authorized between FBI officials and a journalist. But McCabe, who was fired two days before his planned retirement, said the decision was politically motivated, and suggested Trump is trying to taint his integrity as a potential witness in the Russia probe.

Graham said Sunday the Senate Judiciary Committee, to which he belongs, should host a hearing with Sessions testifying about why he fired McCabe. He also said McCabe should have an opportunity to defend himself before Congress.

“We owe it to the average American to have a hearing in the Judiciary Committee for Mr. Sessions to come forward with whatever documentation he has about the firing and give Mr. McCabe a chance to defend himself," Graham said. "When it comes to this issue, we need as much transparency as possible and make sure it [McCabe’s firing] wasn't politically motivated.”