On Saturday, Donald Trump did something he’d never done before, something his closest advisers had warned him not to do: He tweeted Robert Mueller’s name.

But what seemed like a frantic, even panicked, bit of late-night lashing-out is actually a sign of things to come. Multiple aides and Trump confidants tell The Daily Beast that they believe this will not be the last time the president goes after the Justice Department special counsel on his frenetic Twitter feed. And that’s making some of them nervous.

The president, those close to him say, is determined to more directly confront the federal probe into his campaign’s potential role in alleged Russian election interference, even if it means exacerbating his legal standing amid an investigation that has already ensnared some of his most senior campaign and White House aides.

Two sources who speak regularly with Trump said they had noticed an uptick in recent months in the frequency of the annoyance the president would express regarding Mueller and his team, and the irritation at the deluge of negative news stories regarding the probe.

Last week, for instance, The New York Times reported that Mueller had subpoenaed the Trump Organization to turn over documents, some pertaining to Russia—a demand for personal financial details that the president famously said would be crossing a “red line” in an interview with the Times last year.

Still, on Sunday, White House lawyer Ty Cobb blasted out a statement to reporters that simply assured, “in response to media speculation and related questions being posed to the Administration, the White House yet again confirms that the President is not considering or discussing the firing of the Special Counsel, Robert Mueller.”

The White House press office did not immediately respond to a request for comment. But some of the president’s more prominent allies—on Capitol Hill, in the administration, and in pro-Trump media circles—looked on with unease as Trump attempted to undermine the special counsel’s probe.

“I think it’s a very delicate balance,” former Rep. Jack Kingston (R-GA), a top Trump media surrogate, told The Daily Beast on Sunday morning. “There’s nothing unusual about sending signals, but I think because of the highly charged nature of the situation… [He should] make sure his lawyers know what he’s up to.”

“It’s an area full of landmines, so tread carefully,” Kingston added.

This advice, of clearing tweets with lawyers and advisers, has been recommended by various people close to Trump before. And it has consistently been ignored by the president. That’s left aides searching for more creative ways to try to insulate the president from his own worst instincts.

On Sunday, that appeared to mean shepherding him to the golf course, where he wouldn’t be tempted to weigh in on cable news broadcasts about developments in the special counsel investigation.

The dismissal of Mueller or Deputy Attorney General Rod Rosenstein, the DOJ official overseeing the investigation, is a possibility now gripping the halls of power in Washington. Though Trump has flirted with the idea of axing Mueller multiple times—according to The New York Times, he ordered that Mueller be fired last year only to renege when his White House counsel, Don McGahn, threatened to quit—he has never before been so publicly aggressive about it.

Over the weekend, one of Trump’s attorneys, John Dowd, told The Daily Beast that Rosenstein should shut down the investigation just hours before Trump began targeting Mueller on Twitter. Dowd insisted, after the fact, that he had said as much in his personal capacity. But in his first email to The Daily Beast he had said he was speaking as Trump’s counsel. And the president’s subsequent tweets suggested strongly that it was not coincidental. Twice, over the weekend, Trump went after Mueller by name—once while live-tweeting Fox & Friends from the White House—declaring that “the Mueller probe should never have been started,” and the other by claiming that the special counsel has “13 hardened Democrats... and zero Republicans” on his team. In fact, Mueller himself is a Republican.

Though questions about the longevity of the Mueller probe have swirled for months, Trump’s tweet, along with Dowd’s comments on Saturday, forced prominent lawmakers to once again weigh in on the possibility that the administration would attempt to shut down the investigation.

Congressional Republicans have publicly warned Trump on multiple occasions that it would be politically toxic if he fires Mueller—but they haven’t thrown their weight behind bipartisan legislative pushes aimed at shielding Mueller from the president’s whims, arguing that Trump’s statements do not constitute a real threat to the special counsel.

Even Sen. Lindsey Graham (R-SC), who co-authored one of those legislative backstops, had begun backing away from his own proposal in recent months. On Sunday, however, the South Carolina Republican appeared to harden his position and signal a potential revival of his legislative effort.

“If he tried to [fire Mueller], that would be the beginning of the end of his presidency,” Graham said on CNN’s State of the Union on Sunday. “I think it’s very important [Mueller] be allowed to do his job without interference, and there are many Republicans who share my view.”

One of those Republicans, it seems, is Rep. Trey Gowdy (R-SC), the chairman of the House Oversight Committee—a top House conservative on judicial matters who recently announced his retirement from Congress.

“If you look at the jurisdiction for Robert Mueller, first and foremost, what did Russia do to this country in 2016? That is supremely important and it has nothing to do with collusion,” Gowdy said on Fox News Sunday . “So to suggest that Mueller should shut down and that all he is looking at is collusion—if you have an innocent client, Mr. Dowd, act like it.”

While Trump cannot directly fire Mueller, he can order Rosenstein to carry it out. Rosenstein, who appointed Mueller and is overseeing the investigation because Sessions recused himself from matters relating to the 2016 election, has spoken favorably of him on multiple occasions. Gowdy appeared to suggest that if Trump moved to fire Mueller, both Rosenstein and Sessions would be ousted, too.

“I think the president’s going to have a really difficult time nominating and having approved another attorney general,” Gowdy said.