Amid recent chatter that Trump could fire special counsel Robert Mueller, Sens. Lindsey Graham (R-SC) and Jeff Flake (R-AZ) both suggested Tuesday that if the president took that step, impeachment would be the appropriate response.

Graham and Flake’s commitments to this position were hardly rock-solid and may well not be shared by very many other Republicans in the Senate (or the House of Representatives, which is where the impeachment process would have to begin). Still, the statements are a significant warning to Trump from two members of his own party about how Mueller’s dismissal could end for him.

First, when asked by radio host Hugh Hewitt Tuesday morning if firing Mueller would be an impeachable offense, Graham responded, “Probably so, if he did it without cause.”

“I think what the president will have done is stopped an investigation in[to] whether or not his campaign colluded with the Russians, what effect the Russians had on the 2016 campaign. I can’t see it being anything other than a corrupt purpose,” Graham added. “To stop investigation without cause, I think, would be a constitutional crisis.”

Later in the day, the Washington Post’s Robert Costa asked Flake a similar question, and the Arizona senator responded, “To fire Mueller without cause, I don’t know if there is any other remedy left to the legislative branch.”

Flake went on: “If [Trump] fires [Mueller] without cause, how different is that from what Nixon did with the Saturday Night Massacre? He left before impeachment came, but that was the remedy then and that would be the remedy now.”

Afterward, Flake sent this tweet:

We are begging the president not to fire the special counsel. Don't create a constitutional crisis. Congress cannot preempt such a firing. Our only constitutional remedy is after the fact, through impeachment. No one wants that outcome. Mr. President, please don't go there. — Jeff Flake (@JeffFlake) March 20, 2018

Both Graham and Flake have in the past proven unusually willing to criticize Trump compared with other Republican politicians, though in recent months, Graham has tended to take a friendlier tone. Flake wrote a book criticizing Trump last year, but then decided to retire when it looked like he’d lose his primary this year.

Other Republicans didn’t go so far as Graham and Flake, but Senate Majority Leader Mitch McConnell did say that “Bob Mueller should be allowed to finish the job” and called him “an excellent appointment.”

It would take the support of a majority in the House of Representatives to impeach Trump, and then two-thirds of the Senate to remove him from office.