“If an early supporter like this is thrown under the bus, then who is safe?” asked Mark Krikorian, executive director of the Center for Immigration Studies and a supporter of stricter immigration policies like those promoted by Mr. Sessions. “You can imagine what the other cabinet secretaries are thinking.”
That may not bother Mr. Trump, who seems to thrive on slapping those close to him and keeping them on edge. Notoriously fickle, he left Sean Spicer, the White House press secretary, on the hook for six months before his resignation last week. Reince Priebus, the chief of staff, is still on the bubble and said to be looking for a graceful exit of his own.
But that does not necessarily mean that Mr. Trump will push out Mr. Sessions. Stephen K. Bannon, the chief White House strategist, was in trouble a few months ago, but survived. For Mr. Trump, the former reality-show star, the suspense over Mr. Sessions is a season-ending cliffhanger: Stay tuned to see whether he gets voted off the island.
Mr. Trump raised the dramatic tension on Tuesday with a morning message on Twitter: “Attorney General Jeff Sessions has taken a VERY weak position on Hillary Clinton crimes (where are E-mails & DNC server) & Intel leakers!”
Mr. Trump repeated at a news conference later in the day what he told The New York Times last week: that he would not have appointed Mr. Sessions if he had known that the attorney general would step back from the Russia inquiry. “I am disappointed in the attorney general,” he said in the White House Rose Garden.
In an interview with The Wall Street Journal, Mr. Trump dismissed the notion that Mr. Sessions, as the first senator to endorse his candidacy, deserved special loyalty.
“When they say he endorsed me, I went to Alabama,” Mr. Trump said. “I had 40,000 people. He was a senator from Alabama. I won the state by a lot, massive numbers. A lot of the states I won by massive numbers. But he was a senator, he looks at 40,000 people and he probably says, ‘What do I have to lose?’ And he endorsed me. So it’s not like a great loyal thing about the endorsement.”
The loyalty Mr. Trump was looking for, aides said, was about protecting him now that he is in office. “The president wants his cabinet secretaries to have his back,” said Anthony Scaramucci, the new White House communications director.
Mr. Sessions, however, is more than just another employee who has fallen out of favor with a volatile boss. No cabinet member is more closely associated with the conservative nationalism that helped propel Mr. Trump to the White House. For conservatives skeptical of Mr. Trump, Mr. Sessions has been an insurance policy in an administration stacked with suspect New Yorkers, relatives and Wall Street bankers.
Breitbart News, the conservative nationalist outlet once led by Mr. Bannon, reflected anger on the right. “Trump vs. Trump: Potus Endangers Immigration Agenda,” its lead headline read on Tuesday. One article said the attack on the attorney general “only serves to highlight Trump’s own hypocrisy” while another said Mr. Sessions’s ouster “would be a devastating blow” to the nationalist-populist movement.
The division was clear, too, on the Drudge Report, the conservative-leaning website whose double-barreled headline on Tuesday was “Sessions in Dog House; Republicans on Brink of Civil War.”
Frustration among conservatives has been building for some time. Weeks ago, Mr. Bannon brought Ann Coulter, the firebrand pundit, to see Mr. Trump, according to two people briefed on the visit. Ms. Coulter railed at the president that he needed to focus more on his core supporters.
On Capitol Hill, where Mr. Sessions served for 20 years, Senator Mitch McConnell, the majority leader, and other Republicans came to his defense. “Sessions is not weak,” said Senator Richard C. Shelby, a former colleague from Alabama. “He’s strong. He’s a man of purpose, integrity, substance.”
Senator Lindsey Graham of South Carolina said: “Jeff Sessions is one of the most decent people I’ve ever met in my political life. He’s a rock-solid conservative, but above else he believes in the rule of law.”
Democrats, never fans of Mr. Sessions, nonetheless warned that Mr. Trump should not dump him and install a more sympathetic replacement during the coming Senate break. “Democrats will never go along with the recess appointment,” said Senator Chuck Schumer of New York, the minority leader. In a challenge to Republican leaders, he said, “I can’t imagine they would be complicit in creating a constitutional crisis.”
As for Mr. Sessions, who does not have a Twitter account, he has stayed out of the fray since he said on Friday that he wanted to continue working “under Trump’s direction.” On Tuesday, Mr. Sessions announced a new measure to withhold funding from states and cities that do not cooperate with federal immigration authorities.
Critics said Mr. Trump’s assault on Mr. Sessions undermined the traditional independence of the Justice Department. “It is an extraordinary departure from how the relationship of the White House and the Department of Justice is supposed to operate and has operated under administrations of both parties,” said Matthew S. Axelrod, a department official under President Barack Obama.
Some Democrats criticized Mr. Sessions for remaining quiet. “The fact that the president has talked about politicizing investigations and the attorney general has nothing to say?” said Matthew Miller, a department spokesman during the Obama administration. “I thought that was a really, really bad moment for him as attorney general.”
The question remains whether it might be one of his last moments as attorney general.