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 (D-Del.) issued a stark warning to President Trump on Sunday, saying firing special counsel Robert Mueller would cross a line and spur bipartisan pushback in the Senate.

"I think if the president should fire Robert Mueller abruptly, that would be crossing a big line, and I think you would be seeing strong bipartisan action from the Senate which might include our reinstating him or our hiring him to continue to conduct that investigation on behalf of Congress," Coons said on "ABC This Week."

Coon's comments come after he and 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 (R-N.C.) introduced bipartisan legislation dubbed the Special Counsel Integrity Act that would allow Mueller or any special counsel to challenge their hypothetical firing in court.

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Sens. Cory Booker (D-N.J.) and Lindsey Graham (R-S.C.) are working on separate legislation that would hinder the president's ability to fire Mueller.

Trump has repeatedly lashed out at Mueller throughout the investigation into Russian election interference, accusing the special counsel of having conflicts of interest.

The federal probe includes scrutiny of Trump administration officials who met with Russians during the 2016 presidential campaign.

The president told The New York Times that he had done nothing wrong and "a special counsel should never have been appointed in this case.”

Trump's lawyer Jay Sekulow has publicly suggested the president could fire Mueller if he saw fit.

“The president has authority to take action,” Sekulow told ABC News. “Whether he would do it is ultimately a decision the president makes.”