The Senate majority’s No. 2 leader has given President Donald Trump one of the strongest pushbacks from any Republican in Congress this year: Firing Attorney General Jeff Sessions could bring to a halt GOP cooperation with the administration’s legislative agenda.

“Well, it’s the president’s prerogative, but he is then going to jeopardize, potentially, his ability to get anything else done here,” Majority Whip John Cornyn told reporters Wednesday. “And I don’t think that should be his desire or preference.”

Cornyn, a former Texas attorney general and justice on the state Supreme Court, said he continues to view Sessions as “doing just a fine job” running the Justice Department and as someone who “did the right thing” — for that sake of his own credibility and that of the department — by recusing himself from the FBI’s investigation into Russian election meddling.

Sessions did so after conceding he had contacts with Russia during the 2016 campaign, when he was a senator from Alabama and one of Trump’s most prominent surrogates and political counselors.

The Senate leader’s warning to the White House marked one of the very few times, since Trump became president six months ago, that a GOP lawmaker of any consequence has suggested inflicting any sort of political punishment for the president’s out-of-bounds behavior.

And Trump’s treatment of Sessions is unprecedented by almost any measure. Not only do presidents customarily dismiss Cabinet secretaries who displease them rather than demean them almost daily, but Sessions was also the first senator to endorse his candidacy.

He therefore represents one of the most influential links between the White House and Capitol Hill, at a time when Trump’s entire legislative program seems to be just a couple of votes away from near oblivion, as well as an important link between the president and several of the influential conservative groups who boosted Trump’s improbable candidacy.

Trump’s steady stream of social media taunts of Sessions continued into a second week on Wednesday. Within an hour of the attorney general’s arrival at the West Wing for some routine meetings, Trump once again took to Twitter to make clear his anger has not abated.

“Why didn’t A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got big dollars ($700,000) for his wife’s political run from Hillary Clinton and her representatives,” he tweeted. “Drain the Swamp!”

Why didn’t A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got….

— Donald J. Trump (@realDonaldTrump) July 26, 2017

…big dollars ($700,000) for his wife’s political run from Hillary Clinton and her representatives. Drain the Swamp!

— Donald J. Trump (@realDonaldTrump) July 26, 2017

Trump was not supposed to be present at the meeting Sessions was at, and the two have not been face-to-face or even spoken in more than a week.

“I would fire somebody that I did not believe could serve me well rather than trying to humiliate him in public, which is a sign of weakness,” GOP Sen. Lindsay Graham of South Carolina told reporters.

Graham and several other Republican senators encouraged Sessions to remain on the job, sustaining the wall of support he’s enjoyed from former colleagues in recent days. Not one of them has publicly taken Trump’s side.

Senate Democrats, too — including several who are Sessions’ ideological opposites — are urging him to stay in his position unless Trump explicitly orders him to leave.

Their political calculation is that the president firing his attorney general could provide the spark that starts focusing more  public attention on Trump’s legal and ethical challenges in the Russia matter, especially if the president then moves to name a new attorney general seen as willing to dismiss special counsel Robert S. Mueller III.