A bipartisan group of senators have a bill that would put barriers in place in the event President Trump tries to oust special counsel Robert Mueller.

The Senate Judiciary Committee is advancing the bill, despite opposition from Republican leadership in the House and Senate.

But Judiciary members are still at odds over an unseen amendment that Democrats say could undermine the special counsel's investigation.

WASHINGTON — A bipartisan group of senators have finally merged their two bills that aim to protect Robert Mueller, the special counsel investigating Russian meddling in the 2016 election.

But the spur of momentum to put barriers in place in the event President Donald Trump tries to oust Mueller might not be enough.

Trump has already reportedly attempted to fire Mueller once, but backed down under advice of his staff. The president has also launched Twitter tirades against Mueller, which earned a collective shrug from lawmakers. In addition, the White House said Tuesday they believe Trump has the authority to fire Mueller.

But now Republicans are less certain that Trump will not wake up one morning and try to oust Mueller or Deputy Attorney General Rod Rosenstein, who oversees the probe.

The bill, titled The Special Counsel Independence Integrity Act, would immediately fight an unjust firing of the special counsel in court. It combines two previous bills and is backed by Republican Sens. Lindsey Graham and Thom Tillis alongside Democratic Sens. Chris Coons and Cory Booker.

Iowa Sen. Chuck Grassley, who chairs the Judiciary Committee, has vowed to take up the bill next week, signaling urgency. Despite letting the bill be considered, Grassley has not committed to supporting it.

Grassley also has an amendment to the bill, which has yet to be made public, that Democrats worry could severely undermine the investigation. That infighting in the committee could stymie any momentum the legislation may have gained in the past several days.

"I had mostly Democrats ask me for [the bill], so all I see is by them using this as excuse that they're just delaying when I'm trying to accommodate them," Grassley told Politico in an interview. "I think they ought to see our goal is not injurious to what we're trying to accomplish."

And Republican leaders in both chambers have made clear they do not think any bill is necessary.

"I have no reason to believe that that's going to happen," House Speaker Paul Ryan said Wednesday regarding the prospect of Trump ousting Mueller. "I have assurances that it's not, because I've been talking to people in the White House about it."

Senate Majority Whip John Cornyn told reporters on Thursday that the president wouldn't sign the bill and that "the question is is it constitutional?"

Thursday afternoon, Trump's personal Twitter account posted a swipe at reports that former White House strategist Steve Bannon was revamping his push to have Trump push out Mueller.