Republican senator and longtime Trump ally Lindsey Graham (R-South Carolina) said that he has not ruled out the possibility of President Donald Trump‘s impeachment during an interview that aired Sunday.

Graham was asked on Axios on HBO if he could support impeachment if more evidence comes out.

“Sure, I mean show me something that is a crime,” Graham replied. “If you could show me that, you know, Trump actually was engaging in a quid pro quo outside the phone call, that would be very disturbing.”

Graham is referencing Trump’s phone call with the president of Ukraine, in which he seemingly asked their government to investigate his political rival, Joe Biden. The call has been at the forefront of the Democrats’ impeachment inquiry, and has been criticized as an abuse of his power.

The term “quid pro quo” has been thrown around, as democrats investigate whether Trump withheld military aid in exchange for Ukraine launching a political investigation benefiting Trump.

Last Thursday, acting chief of staff Mick Mulvaney told reporters there was a quid pro quo and “we do that all the time” in foreign policy.

“Did he also mention to me in [the] past the corruption related to the DNC server? Absolutely,” Mulvaney said during a news conference. “No question about that. But that’s it, and that’s why we held up the money.”

He later tried to walk back his comments in a statement that said “there was absolutely no quid pro quo between Ukrainian military aid and any investigation into the 2016 election.”

Graham’s interview was taped Tuesday, two days prior to Mulvaney’s comments.

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His admission of a quid pro quo has alarmed many GOP lawmakers.

Sen. Lisa Murkowski (R-Alaska) criticized the move, saying “You don’t hold up foreign aid that we had previously appropriated for a political initiative. Period.”

Rep. Francis Rooney (R-Florida) told CNN, “Whatever might have been gray and unclear before is certainly quite clear right now that the actions were related to getting the Ukraine to do some of these things.”

Rooney joined Graham in saying he would not rule out the possibility of impeachment.

“I’m not going to say anything about that until all the facts are in,” he said. “I remember too many people saying, ‘Oh, this is a witch hunt against Richard Nixon,’ and come to find out it wasn’t a witch hunt.”