WASHINGTON -- A bipartisan group of four senators is moving to protect special counsel Robert Mueller's job as President Trump publicly muses about firing him. GOP Sens. Thom Tillis of North Carolina and Lindsey Graham of South Carolina and Democratic Sens. Chris Coons of Delaware and Cory Booker of New Jersey introduced legislation Wednesday that would give any special counsel a 10-day window to seek judicial review of a firing, according the Associated Press, which cited two people familiar with the legislation. They weren't authorized to discuss the bill ahead of its release, and requested anonymity.

The legislation, which combines two bipartisan bills introduced last summer, signals escalating concerns in Congress over whether Mueller's job is safe. On Monday, Mr. Trump fumed about the FBI raid of the office of his personal attorney, Michael Cohen. Mr. Trump has also reportedly privately pondered firing Deputy Attorney General Rod Rosenstein and publicly criticized Mueller and his Russia probe.

In addition to investigating potential ties between Russia and the Trump campaign, Mueller is examining whether the president's actions constitute obstruction of justice. As the investigation has worn on, Mr. Trump has repeatedly called it a "witch hunt." And on Monday, after the Cohen raid, the president said it was "an attack on our country." The raid was overseen by the U.S. Attorney's office in Manhattan and was based in part on a referral from Mueller.

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Similar bills were introduced in August, when Mr. Trump first began criticizing the Mueller probe. Both Tillis and Graham had been quiet for months on whether the legislation was still needed as Democrats continued to push for a bill. Both Republicans said they didn't think Mr. Trump would really move to fire Mueller. But the senators moved to push out a new, combined bill in the hours after Mr. Trump's tirade.

Under the legislation, the expedited review would determine whether the special counsel was fired for good cause. The bill would also ensure that any staff, documents and other investigation materials were preserved as the matter was pending.

It's unclear if it could ever become law. Such legislation is unlikely to move through the House, and many Republicans in the Senate still expressed confidence Tuesday that Mr. Trump would not fire the special counsel.

"I don't think he's going to be removed," said Senate Majority Leader Mitch McConnell, R-Ky. "I think he'll be allowed to finish his job."

Still, senators have publicly and privately let the White House know that firing Mueller would be a mistake, said the No. 2 Republican, Sen. John Cornyn of Texas.

"There would be serious repercussions," said Sen. Bob Corker, R-Tenn. "I've shared with the president what a massive mistake it would be for him to do this. I've done that in person."

Sen. Chuck Grassley, R-Iowa, the chairman of the Judiciary Committee, said Tuesday on Fox Business News: "It would be suicide for the president to want to talk about firing Mueller. The less the president said on this whole thing, the better off he would be, the stronger his presidency would be."

Democratic leaders have pushed for Republicans to move legislation to protect Mueller.

"Stand up and say what the president is doing is wrong," said Senate Minority Leader Chuck Schumer, D-N.Y. "Make it clear that firing Mueller or interfering in his investigation crosses a red line."

Mr. Trump cannot directly fire Mueller. Any dismissal, for cause, would have to be carried out by Rosenstein, who appointed the counsel in May 2017 and has repeatedly expressed support for him.

But White House Press Secretary Sarah Sanders said in her Tuesday briefing that the president " certainly believes" he has the authority to fire Mueller directly.