White House officials are unable to point to any internal assessment to justify their contention that President Donald Trump has the legal authority to fire special counsel Robert S. Mueller III.

Many Republican and Democratic lawmakers are urging Trump to let the former FBI director complete his investigation of Russian election meddling and possible misconduct by the president and his campaign associates. Those pleas intensified last week when the president and his top spokeswoman signaled the White House has concluded he has the authority to do so.

The legal community is split on whether a sitting U.S. president has the legal authority to remove a special counsel.

Some experts say Justice Department rules that govern the appointment, supervision, conduct and termination of special counsels vest firing authorities in the attorney general. Others contend there is nothing in those rules to preclude a president from giving the termination order.

Watch: White House’s Sanders and Trump Imply Firing Authority Over Mueller

Trump used a Thursday morning tweet to imply he has the authority to fire Mueller. “If I wanted to fire Robert Mueller in December,” he wrote, “I would have fired him.” The president was responding to a New York Times article published the night before that cited sources who said Trump fumed about reports saying the special counsel was looking into his business dealings with Deutsche Bank late last year. He has said any investigation of his business would be a “red line” that would justify Mueller’s removal.

If I wanted to fire Robert Mueller in December, as reported by the Failing New York Times, I would have fired him. Just more Fake News from a biased newspaper!

— Donald J. Trump (@realDonaldTrump) April 12, 2018

Two days prior, White House Press Secretary Sarah Huckabee Sanders told reporters Trump “certainly believes he has the power to do so.” Asked again, she said White House officials have “been advised that the president certainly has the power to make that decision.”

But Sanders then added this cryptic statement about the White House’s conclusion: “I can’t go anything beyond that.” She did not respond to several emails seeking more information.

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What’s more, several other White House aides were unable to point to any internal legal review that led to Trump’s tweet and Sanders’ statements. Such assessments, under previous presidents, typically would have been conducted by the White House counsel’s office.

Multiple Trump aides, however, were unable to point to any such review by White House counsel Donald McGahn and his staff when pressed. Nor could they describe any Justice Department assessment.

With no internal legal assessment, it appears the White House’s conclusion likely is based on scholarly work, op-ed pieces and comments in media appearances by the legal camp that has concluded a sitting chief executive has the power to remove a special counsel.

‘Terrible mistake’

Whether there is an internal legal review to justify the White House’s stance, GOP lawmakers are counseling the president that terminating Mueller would be a mistake.

“It would be a terrible mistake for the president to fire him. It would be bad for the president. It would be bad for Republicans in Congress in the midterms. And, most of all, it would be bad for the American people,” retiring Pennsylvania GOP Rep. Charlie Dent told CNN Monday. “I think he should think very hard about this. It would be a self-destructive act to do that. And it would set off a political crisis if he were to fire Mueller.”

Dent called for Congress to pass legislation protecting Mueller, saying, “One area where we’ve made a mistake in Congress … is we’ve not provided enough robust oversight on the president on some of these issues.” (A bipartisan group of senators has introduced a bill that would do just that, but Speaker Paul D. Ryan is opposed, saying it won’t be necessary because he doubts the president will fire Mueller.)

Such comments come as a new ABC News-Washington Post poll shows 69 percent of those surveyed support the Russia probe. And 64 percent are in favor of Mueller looking at Trump’s business dealings.

The 1999 special counsel guidelines include a section on “conduct and accountability,” stating one can be “disciplined or removed from office only by the personal action of the Attorney General.”

Watch: What’s the Status on the Bill to Protect Mueller?

“The Attorney General may remove a Special Counsel for misconduct, dereliction of duty, incapacity, conflict of interest, or for other good cause, including violation of Departmental policies. The Attorney General shall inform the Special Counsel in writing of the specific reason for his or her removal,” the regulations state. (In the case of the Mueller probe, these authorities were transferred to Rod Rosenstein, the deputy AG, when Attorney General Jeff Sessions recused himself.)

Notably, however, the three-page document never mentions the Executive Office of the President or its specific authorities in relation to a special counsel. Also notable: Sessions has publicly referred to Trump as the country’s top law enforcement official.

Jack Goldsmith, a Harvard Law School professor and co-founder of the Lawfare blog, has concluded there are “good constitutional arguments” in favor of the president simply signing an order that fires Mueller and “abrogates or ignores the special counsel regulations.” But the matter has been unresolved by legal scholars, with Goldsmith also concluding there are “also countervailing arguments grounded in the principle that only the agency head that appoints the officer, and not the president, can remove the officer.”

Goldsmith has floated the notion that Justice Department officials could refuse to abide and challenge any such order in court. “That litigation would be … interesting,” he wrote last year.

The special counsel guidelines were crafted in 1999 by Neal Katyal, who went on to become acting U.S. solicitor general under President Barack Obama. In the late 1990s, he worked in the office of the deputy attorney general as a national security adviser and special assistant to Justice’s No. 2 official.

When contacted Thursday, Katyal declined an interview request. But he did point a reporter to a recent series of Twitter posts he wrote about the matter. In those tweets, Katyal wrote “the regulations do not prevent Trump from firing Mueller.”

While ordinary citizens lack the luxury of simply firing a prosecutor, “things are a bit difft if you happen to be the President,” he wrote, adding presidents possess “the prosecution power” under the U.S. Constitution.

“So prosecutors serve as an extension of the Presidency,” Katyal tweeted. “For that reason, when the regs were drafted, there was a bipartisan consensus that a President could fire a Special Counsel.” But, importantly, he wrote that the regulations were crafted in a way to force a president to disclose his rationale for terminating a special counsel.

The former Obama administration official’s tweet thread isn’t all rosy for Trump. He also contends Mueller’s firing would “immediately prompt a constitutional crisis, the likes of which many of us have not seen in our lifetimes” because “Trump is afraid of the truth coming out.”

1.THREAD. CAN TRUMP FIRE MUELLER? Robert Mueller is a registered Republican nominated by 2 difft Repub. Presidents. With all the renewed attention,I’m outlining how the Special Counsel Regulations (which I drafted for DOJ in 1999) work.This piece details:https://t.co/d3ZCd4TgvY

— Neal Katyal (@neal_katyal) December 18, 2017

‘Firestorm’ ahead?

On Capitol Hill, Dent is not alone in practically pleading with Trump to resist terminating Mueller.

Democratic lawmakers, joined by some prominent Republicans, warned Trump this week not to fire Mueller. Senate Judiciary Chairman Charles E. Grassley of Iowa said in a television interview that doing so would amount to political “suicide” for Trump. Democratic Sen. Richard Blumenthal of Connecticut, a member of that panel, said Tuesday there would be a “firestorm” on Capitol Hill if the president tries to terminate Mueller.

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Matt House, a spokesman for Senate Minority Leader Charles E. Schumer, responded to Sanders’ assessment Tuesday with a narrow reading of the Justice guidelines, saying they “could not be more clear.”

“The president does not have the authority to remove Special Counsel Mueller,” House wrote in a statement. “Because of the attorney general’s recusal, only Deputy AG Rosenstein could remove the special counsel, and it would have to be for good cause.”

Preet Bharara — whom Trump fired as U.S. attorney for the Southern District of New York, reportedly over fears he would be disloyal — agreed, saying last week in a television interview that the special counsel statute does not give the president power to terminate Mueller.

The legal murkiness around the Justice regulations underscores how Trump firing Mueller would quickly morph into a political matter.

“I think it would be a constitutional crisis,” House Minority Leader Nancy Pelosi said Thursday when asked if such a move would be grounds for impeachment proceedings in that chamber.

She added that if Trump fired Rosenstein, it would be viewed the same way — as an effort to thwart Mueller’s probe.

On Thursday, at the end of a Rose Garden event on the Republican tax bill and other issues, reporters shouted questions at Trump about whether he plans to fire Mueller or Rosenstein. A participant seated between the media and president shot back that perhaps the president should fire those reporters.

The president stood on the colonnade near the Oval Office and smiled as he gave a quick wave to his invited guests. Reporters persisted. But Trump did not provide the answers that likely will shape the remainder of his presidency.

Lindsey McPherson contributed to this report.