Sen. Lindsey Graham (R-SC) on Tuesday said that it would “probably” be an impeachable offense if President Donald Trump fired special counsel Robert Mueller “without cause.”

“If the President fired Robert Mueller, do you think that would be an impeachable offense?” conservative radio host Hugh Hewitt asked the senator in an interview.

“Probably so, if he did it without cause, yeah,” Graham replied.

“Now Angus King said no, last hour,” Hewitt said. “Why do you think it would be?”

“Well, I think what the President will have done is stopped an investigation into whether or not his campaign colluded with the Russians, what effect the Russians had on the 2016 campaign,” Graham said. “I can’t see it being anything other than a corrupt purpose.”

Later in the interview, asked whether congressional Republicans would be willing to impeach Trump, Graham compared the situation to a hypothetical involving former President Barack Obama.

“Let’s say that Obama fired somebody,” Graham said. “I think we’d all have a different view on the Republican side. A high crime and misdemeanor in the Constitution is a fairly vague term. But what is at the essence of impeachment is a check and balance on a President, right, who’s gotten out of their lane, who changed the rule of law and basically turns it upside down.”

He said he could not “think of a more upsetting moment in the rule of law to have an investigator looking at a President’s campaign as to whether or not they colluded with a foreign government, what kind of crimes may have been committed.”

“I’ve seen no evidence of collusion, but to stop investigation without cause, I think, would be a Constitutional crisis,” Graham said.

Near the end of the interview, he recalled the way former President Bill Clinton’s legal team attacked then-independent counsel Kenneth Starr.

“I’m just saying there’s a line you can’t cross,” Graham said. “You can’t fire the guy without cause.”

Graham has supported legislation to protect special counsels, and said on Sunday that if Trump fired Mueller it would “be the beginning of the end of his presidency, because we’re a rule of law nation.”