Congressional Republicans on Tuesday warned President Trump not to fire Attorney General Jeff Sessions, fearing it could be the first step in an attempt to kill the federal investigation into Russian meddling in the 2016 elections.

Republicans have tried mightily to ignore Trump's politically-charged tweets and the rest of the drama coming from the White House, leaving the Russia probe, which could implicate the president or his campaign, to their colleagues on the House and Senate intelligence committees that are running parallel inquiries.

But they made an exception for Sessions, their former colleague, admonishing the White House that relieving the attorney general and moving to dismiss special counsel Robert Mueller and quash his investigation could force them off the sidelines and spark a confrontation with Congress they would rather avoid.

"All hell would break loose," Rep. Mike Simpson, R-Idaho, said in an interview with the Washington Examiner.

"If he fired Mueller, that would be a problem. It wouldn't pass the smell test," added a second House Republican, who requested anonymity in order to speak candidly. "The American people would demand we do something."

Sessions recused himself from the Russia investigation months ago because of the prominent role he played in Trump's campaign. The Alabama Republican, then a veteran senator, was an early supporter and crucial validator when many on the Right still questioned his conservative credentials.

Later, after Trump unceremoniously fired James Comey as FBI director in part because of his handling of the Russia probe, Deputy Attorney General Rod Rosenstein appointed Mueller, a former FBI director respected by Republicans, to assume control of the investigation as special counsel.

Several weeks later, beginning last week, Trump erupted at Sessions in a series of interviews and public remarks, questioning his personal integrity and professional acumen. The president said Sessions never should have recused himself, called him weak and charged that the only reason the then-senator endorsed his campaign was because he wanted attention.

"It's not like a great loyal thing about the endorsement," Trump told the Wall Street Journal. "I'm very disappointed in Jeff Sessions."

"Attorney General Jeff Sessions has taken a VERY weak position on Hillary Clinton crimes (where are E-mails & DNC server) & Intel leakers!" Trump said in a Tuesday morning tweet, leaving out the fact that he said after the election that he did not want to target his Democratic rival.

Republicans on Capitol Hill rushed to Sessions' defense, among them Republicans from Alabama, where Trump remains extremely popular.

Sen. Luther Strange, R-Ala., who is chasing Trump's endorsement in the competitive Aug. 15, special Senate election primary, was compelled to take a veiled shot at the president for the humiliating way he has publicly pondered whether to fire Sessions.

"Jeff Sessions is my mentor, a great friend, and a man of the utmost integrity. His example of leadership inspired me to run for public office in Alabama, and continues to merit the admiration of his team at DOJ, his former colleagues in the Senate, and our great state," Strange, who was appointed to fill Sessions' seat on a temporary basis, said in a statement.

"Jeff and President Trump are trying to make America great again," he continued. "And it's a privilege to work along side both to accomplish the Trump agenda for the American people, and we need to stop letting the media distract us from that agenda."

The underlying concern is that dumping Sessions could lead to eliminating Mueller.

In Trump's interview with the New York Times last week that began the public tongue-lashing of Sessions, he warned the special counsel, a former FBI director respected on both sides of the aisle, to stay away from probing his personal and business financial records.

That's a near impossibility in an inquiry of this magnitude. Trump never released his tax returns, and any connections to Russia are sure to be reviewed to examine the specter of collusion with Moscow.

It's obvious Republicans have no appetite to rebuke the president, fearing a revolt of their own voters at home — many who side with Trump on the Russia matter — and anxious for the turbulence it would cause between now and midterm elections 15 months away. But they conceded in interviews that Mueller's dismissal would necessitate action of some sort, although they were unclear on what form it might take.

It could range from stronger verbal denunciations to more aggressive oversight hearings to passage of laws, like a bill that passed Tuesday, that limit Trump's ability to maneuver without congressional approval. Impeachment proceedings are off the table unless the president commits a crime, GOP insiders said.

"There would have to be a smoking gun," a former Republican congressional aide said. "If he fires Mueller it would be a big deal and there would oversight hearings but it would be similar to Comey. I don't think it would near impeachment. I think there would have to be proof of collusion or breaking the law."

For conservatives, Sessions is an ideological touchstone in an unpredictable administration. He's an immigration hawk who adopted this position long before they were ascendant in the Republican Party, and he's viewed as insurance against Trump drifting left on border security and illegal immigration.

His circle of friends in Congress reaches beyond these circles, however. Many Republicans disagree with his positions on immigration and trade, but always appreciated his professionalism and honesty. In a chaotic White House, Sessions is a dependable ally.

Trump firing the attorney general could cause a breakdown in relations that area already rocky and highly transactional, Republican senators and congressional aides across Capitol Hill told the Washington Examiner in private conversations.

"Jeff's a good friend of mine. He stuck his neck out early for the president, which I have a lot of respect for, and I think that will pay off for him in the long run," Sen. Johnny Isakson, R-Ga., added.