Sen. Lindsey Graham Lindsey Olin GrahamMcConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-S.C.) on Sunday warned of the consequences for President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE if he tries to fire special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE.

Graham was asked on CNN's "State of the Union" if he is worried Trump is preparing to order Mueller's firing.

"If he tried to do that, that would be the beginning of the end of his presidency, because we're a rule of law nation," Graham said.

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Graham said Mueller is following the evidence where it takes him.

"I think it's very important he be allowed to do his job without interference and there are many Republicans who share my view," Graham said.

Trump has repeatedly dismissed the special counsel's probe into Russia's election interference and possible ties between his campaign and Russia as a "witch hunt" and has denied collusion.

Graham's comments come after Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE on Friday fired former FBI Deputy Director Andrew McCabe Andrew George McCabeGraham: Comey to testify about FBI's Russia probe, Mueller declined invitation Barr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' GOP votes to authorize subpoenas, depositions in Obama-era probe MORE.

In recent days, Trump has taken to Twitter to attack the Mueller probe.

On Saturday, he tweeted the probe "should never have been started in that there was no collusion and there was no crime."

"It was based on fraudulent activities and a Fake Dossier paid for by Crooked Hillary and the [Democratic National Committee], and improperly used in [Foreign Intelligence Surveillance Act] COURT for surveillance of my campaign. WITCH HUNT!" Trump tweeted.

He also called McCabe's firing a "great day for the hard working men and women of the FBI."