Members of Congress were aghast on Thursday after President Donald Trump suggested that he would move to fire special counsel Robert Mueller if his investigation into Russia’s election meddling turned toward Trump’s finances.

But those same members said that they were unable to preemptively shield Mueller from the threat of presidential interference.

“That’s not our lane. It’s an independent counsel. So he should be independent. And we should do our job and the two things should not be connected,” Sen. Martin Heinrich (D-N.M.) told The Daily Beast. Heinrich sits on the Senate Select Committee on Intelligence, which is also investigating Russian meddling and potential collusion between Trump associates and Russian operatives.

Sen. Tom Carper (D-DE) also acknowledged that Congress could not prevent the president from dispensing of Mueller. In a reflection of the powerlessness of the legislative branch in such a scenario, he humorously suggested that a robust social-media campaign might do the trick.

“I think that maybe we could have a tweet-storm—a tweet-storm directed at the president that all of us, Democrats and Republicans, would tweet the same message to 1600 Pennsylvania Ave. and say: Mr. President, don’t you dare,” Carper said with a laugh.

Mueller enjoys bipartisan support on the Hill, where lawmakers expressed continued confidence in his ability to oversee the investigation. But as Heinrich noted, that investigation remains under the purview of the executive branch, which leaves it vulnerable to Trump’s whims. And that’s not a particularly secure place to be.

In an interview Wednesday with The New York Times, Trump issued a stark warning to Mueller to avoid looking into look into his personal finances.

“I think that’s a violation. Look, this is about Russia. So I think if he wants to go, my finances are extremely good, my company is an unbelievable successful company,” Trump said. When asked if he would fire Mueller over an examination of his finances, Trump left the door open.

“I can’t answer that question because I don’t think it’s going to happen,” the president added.

White House Deputy Press Secretary Sarah Huckabee Sanders told reporters on Thursday that the president “has no intention” to fire Mueller “at this time.” But in recent weeks, the president and his legal team have left the door open. Jay Sekulow, a member of Trump’s outside legal team, said the president “ has authority to take action” if he deems it necessary.

While Congress can do nothing to stop Trump from ousting Mueller, they could make such a move politically painful. Lawmakers on Thursday said that allegations of obstruction of justice would grow louder if Mueller is axed, and they predicted that there would be greater discontent with the president among the Republican rank-and-file in Congress.

“I think that the statements that some Republicans like Lindsey Graham (R-S.C.) have made—saying that that would be a catastrophically foolish error with massive consequences for the administration—have gone a long way to signal that there would be very bad things that follow if he tried that stunt,” Sen. Sheldon Whitehouse (D-R.I.), a member of the judiciary committee, told The Daily Beast.

Sen. Bob Corker (R-TN), who chairs the Foreign Relations Committee and has been critical of the Trump administration on issues relating to foreign policy and national security, told The Daily Beast that firing Mueller would be “so far out of bounds,” that he couldn’t “imagine anybody’s even discussing that at the White House.”

Lawmakers could move retroactively to reinstate a Mueller-like probe should Mueller be fired. Sen. Richard Blumenthal (D-CT), a member of the Senate Judiciary Committee, told The Daily Beast that under such circumstances, Congress should consider legislation to re-establish a special counsel or independent commission to oversee the federal Russia probe.

Trump technically can’t fire Mueller directly himself. That power is left to Deputy Attorney General Rod Rosenstein, who first appointed Mueller. In an interview with Fox News on Wednesday, Rosenstein stood by his decision to hire Mueller.

But Trump could fire Rosenstein if the deputy attorney general refuses his order to fire Mueller—a scenario that harkens to the days of Watergate and Richard Nixon, but one that no longer seems entirely unimaginable as Trump’s frustrations have mounted.

In his interview with the Times, Trump lashed out at Attorney General Jeff Sessions—one of Trump’s earliest allies during the 2016 campaign—over his decision to recuse himself from all matters related to the federal Russia investigation, a decision which handed all Russia-related matters to Rosenstein. Trump lamented that Sessions’ recusal led to Mueller’s appointment as special counsel.

Trump has referred to the broader congressional and federal Russia probes as a “witch hunt” and a “hoax,” among other monikers.

Mueller, for his part, doesn’t seem bothered by Trump’s interview or the fact that Congress can’t intervene to immunize him from a presidential axe. On Thursday morning, Bloomberg reported that Mueller had expanded his investigation to include “a broad range of transactions involving Trump’s businesses as well as those of his associates.” Those transactions include purchases in Trump apartment buildings made by Russians, as well as the 2013 Miss Universe pageant which took place in Moscow.

It was conspicuous timing, considering the warning Trump had issued the night before. A spokesman for Mueller did not respond to a request for comment from The Daily Beast, while John Dowd, a lawyer for Trump, told Bloomberg that he was not aware the probe had expanded to include Trump’s business transactions. Dowd said such examinations would be “well beyond the mandate of the special counsel.”

—Sam Stein contributed reporting.