A pair of senators are working on a backup plan to protect Robert Mueller and the investigation into ties between President Trump's campaign and Russia after the president floated the possibility of firing the special counsel.

GOP Sen. Thom Tillis Thomas (Thom) Roland TillisWhat Senate Republicans have said about election-year Supreme Court vacancies Chamber of Commerce endorses McSally for reelection Airline job cuts loom in battleground states MORE (N.C.) and Democratic Sen. Christopher Coons Christopher (Chris) Andrew CoonsBiden promises Democratic senators help in battleground states Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (Del.) introduced the Special Counsel Integrity Act on Thursday, which would let Mueller or any special counsel challenge their firing in court.

The challenge would be heard by a three-judge panel within 14 days. If they aren't able to find "good cause" for the firing, the special counsel would be reinstated.

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“A back-end judicial review process to prevent unmerited removals of special counsels not only helps to ensure their investigatory independence, but also reaffirms our nation’s system of check and balances," Tillis said in a statement.

The bill would be retroactive back to May 17, when Mueller was named as special counsel for the investigation into Russia's election interference, but would also apply to any special counsel named after that date.

Coons added that "ensuring that the special counsel cannot be removed improperly is critical to the integrity of his investigation."

Under the legislation, only the attorney general, or — in such cases as Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE, who has recused himself in the investigation — the most senior Justice Department official, could discipline or fire a special counsel.

It would also codify existing Justice Department rules that the special counsel can only be removed for "misconduct, dereliction of duty, incapacity, conflict of interest, or other good cause, like a violation of departmental policies."

Such a clause would prevent Trump from firing Mueller.

The legislation comes as Trump has repeatedly lashed out against Mueller's investigation. Allies of the administration have also accused the former FBI director, who is widely respected in Washington, of being too biased to lead the probe.

Sens. Cory Booker (D-N.J.) and Lindsey Graham Lindsey Olin GrahamSenate Republicans face tough decision on replacing Ginsburg Democratic senator calls for eliminating filibuster, expanding Supreme Court if GOP fills vacancy What Senate Republicans have said about election-year Supreme Court vacancies MORE (R-S.C.) are working on separate legislation that would limit Trump's ability to fire Mueller.