Fearing President Donald Trump might finally follow through on firing Robert Mueller, one Republican senator is pushing Congress to act on his bill protecting the special counsel.

Sen. Thom Tillis (R-NC), who has a proposal to check Trump’s power to fire Mueller’s investigation, told reporters he wants the Senate Judiciary Committee to take up his bill.

“It’s a good bill that’s going to have enduring value beyond this presidency. I think the president’s frustrated, I may be if I were in the same position,” Tillis told Politico. “But I do think it’s a bill that’s worthy of a markup in Judiciary and sending it to the floor.”

Trump lashed out against Mueller’s probe Monday, calling it a “witch hunt” and the “end of attorney-client privilege” on Twitter after the FBI raided Trump’s personal lawyer Michael Cohen’s office. Trump told reporters “many people” have told him to fire Mueller, adding, “we’ll see what happens.”

There are currently two bipartisan proposals — one from Tillis and Coons and another from Sens. Lindsey Graham (R-SC) and Cory Booker (D-NJ) — that would put the decision to fire Mueller in front of a three-judge panel in federal courts. Both pieces haven’t had much momentum.

Many admit Trump’s attacks are getting “more intense.” But as Sen. Mike Rounds (R-SD) said Tuesday, when it comes to actually protecting Mueller, congressional Republicans are quick to come up with excuses.

Asked if Congress should act, Sen. John Kennedy (R-LA) told Vox recently he is “not sure it’s constitutional for us to tell the president who he can fire and can’t fire.”

Even Sen. Jeff Flake (R-AZ), a perennial Trump critic, said he is “not convinced” the two proposals are constitutional. But conversations with legal experts show it’s not that simple.

“It is exasperating that lawmakers rely on such easily debunked constitutional concerns for political cover,” Steve Vladeck, a constitutional law expert with the University of Texas Austin’s law school, said.

The disagreement comes down to a longstanding scholarly debate about the constitutional separation of powers, a Supreme Court case from the 1980s, and a political environment that leaves Republicans reticent to involve themselves in anything Russia-related.

There are two bills to protect Mueller. Neither would actually prevent Trump from firing him.

Two bills have been proposed in the House and Senate to protect Mueller’s investigation — the Special Counsel Independence Protection Act, from Graham and Booker, and the Special Counsel Integrity Act, from Tillis and Coons — that follow roughly the same framework: They would allow the White House’s decision to fire the special counsel to be put under judicial review.

Currently, the US attorney general can remove the special counsel “for misconduct, dereliction of duty, incapacity, conflict of interest, or for other good cause, including violation of departmental policies.” Because Attorney General Jeff Sessions has recused himself from the investigation, in Mueller’s case, the power falls in the hands of Deputy Attorney General Rod Rosenstein. There is no way for a special counsel to challenge that decision, even if there’s a case for wrongful termination.

These two bills try to fill that gap, establishing some oversight with a three-judge panel (made up of two District of Columbia district court judges and one US Court of Appeals judge). Neither proposal establishes the special counsel as an un-fireable position, nor does either even limit the White House’s power to fire Mueller.

The difference between the bills is when the judicial branch would get involved in the process of firing the special counsel. In the Graham-Booker bill, a special counsel “may only be removed if the Attorney General files an action in the United States District Court” and notifies relevant Senate and House Judiciary committees. In the Tillis-Coons bill, the special counsel must be informed in writing of the specific reason for being fired and is given a course of action to appeal the decision after the fact.

Whoever loses in court could then appeal to the Supreme Court. In practice, both proposals would actually be extremely modest measures, as Jonathan Turley, a legal scholar with George Washington University Law School, points out.

“[Good cause] is almost an unreviewable standard,” he said. “It would be very difficult for a court to review that kind of language. It’s unlikely that this legislation would materially increase protections for Mueller.”

Until now, the Republicans lawmakers who proposed these bills have downplayed the urgency of passing them into law. Graham said he only sponsored the bill to make his position on the Mueller investigation public. But Trump’s latest comments on the investigation has prompted Tillis to push for some action. Yet, each time Trump mounts another attack against Mueller, Republicans raise concerns that the bills might not be constitutional.

The constitutionality of protecting Mueller’s job, explained

So are these proposals to protect Mueller constitutional? The short answer is likely yes — but it’s not so clear-cut.

The conservative argument is that Congress can’t infringe on the executive authority; that constitutionally, the president maintains the power to control who serves in the executive branch. At a Senate Judiciary Committee hearing on the constitutionality of the two special counsel bills in September, which included testimony from legal scholars and experts, John Duffy of the University of Virginia School of Law said the “transfer of removal authority from the Executive to the Judicial Branch is almost certainly unconstitutional” under Booker and Graham’s proposal. Others like Vladeck, however, called the effort appropriate and in line with current legal precedent.

The conservative constitutional concerns go back to the 1988 Supreme Court case Morrison v. Olson, a 7-1 decision that upheld the Independent Counsel Act — a statute passed in the wake of Nixon’s firing of the Watergate special prosecutor that created an investigator role completely independent from the executive branch. Justice Antonin Scalia was the single dissent on the case, arguing that the independent counsel was a clear disruption of the separation of powers:

Frequently, an issue of this sort will come before the Court clad, so to speak, in sheep’s clothing: the potential of the asserted principle to effect important change in the equilibrium of power is not immediately evident, and must be discerned by a careful and perceptive analysis. But this wolf comes as a wolf.

Scalia said that a “governmental investigation and prosecution of crimes is a quintessentially executive function.” Despite the Court’s decision upholding the role of an independent counsel, Congress allowed the act to expire in 1999. In its place, there’s the special counsel, the role Mueller holds, which is largely the same on the merits but is not separate from the administration — the cause for a lot of debate among legal scholars.

“The special counsel is the creation of the attorney general or his designated subordinate; as such, the argument could be that any limitations intrude upon executive authority,” Turley said of the proposals to introduce a judicial review in a possible Mueller firing.

Vladeck says it cuts the other way entirely — that there is more room for protection precisely because the special counsel is under the Justice Department’s control.

“I find this public conversation so frustrating. Two things would have to be true for this to be unconstitutional: First, the Supreme Court would have to overrule Morrison and then go past Morrison and rule in the other direction,” Vladeck said, attributing the debate to a “disconnect between folks on the Hill and conservative and libertarian scholars.”

“The bottom line is Morrison v. Olson is still good law and we drafted our bill with that in mind,” Booker, who is sponsoring one of the proposals, said. “There are plenty of constitutional scholars who agree that our bill is on firm constitutional footing.”

The constitutionality debate is ultimately a political one

If Congress were to pursue a bill to add a layer of oversight to any staffing shake-ups in the Mueller investigation, Turley says there could be a “credible challenge to the bills, and it may be a toss-up when it gets to the Court.” To be sure, Congress doesn’t seem too eager to pursue these bills, and the Supreme Court has rarely overturned decisions made in such recent history.

Even so, this debate over constitutionality speaks to Republicans’ reluctance to actively involve themselves in the Russia investigation — a conversation on Capitol Hill that has the potential to change radically, should Democrats regain a majority in the House or Senate.

There’s no question that Trump has repeatedly pushed the line on attacking Mueller and his investigation. He reportedly tried to push Mueller out last June. Congressional conservatives have rallied around the White House in trying to discredit the investigation and the Russia allegations for months.

Two House Republicans, Ohio’s Jim Jordan and North Carolina’s Mark Meadows, known for their close relationship with Trump, even called for Jeff Sessions to resign for allowing the Russia investigation to get out of hand.

Republican leaders have taken a markedly different tone. Senate Majority Leader Mitch McConnell spoke to the credibility of Mueller’s investigation and said it should be allowed to conclude without any impediments.

Senator have also made clear that the stakes of Trump actually firing Mueller would be very high. Graham said firing Mueller “would be the beginning of the end of his presidency,” and Kennedy added that Trump knows better than to fire Mueller. “He’s too smart,” he said.

And when it comes to actually acting, for Republicans Trump actually firing Mueller is the only red line.