This editorial appeared in The Charlotte Observer.

Last August, Sen. Thom Tillis of North Carolina was concerned enough about protecting Special Counsel Robert Mueller’s investigation that he co-sponsored legislation that would make firing a special counsel subject to review by a three-judge panel.

By January of this year, Tillis’s office said that while he still supported that bill, the matter was no longer urgent because President Trump said he didn’t plan to fire Mueller. A few months later, however, the senator’s concern had apparently resurfaced. Tillis, along with fellow Republican Sen. Lindsey Graham and Democratic Sen. Cory Booker, introduced the Special Counsel Independence and Integrity Act, which would protect Mueller from an increasingly frustrated Trump.

“This bill becoming law would remove that narrative from the conversation,” Tillis said then.

That narrative is now back. Monday, Axios reported that Deputy Attorney General Rod Rosenstein has offered to resign in anticipation of being fired by Trump. Rosenstein will meet with Trump on Thursday. Rosenstein is the top Justice Department official overseeing the Mueller investigation, and his impending departure, if true, prompts some obvious questions about what the president might do next with Mueller. After all, Trump has repeatedly scorned the special counsel and once tried to orchestrate his firing before backing down.

Now, more than ever, Americans need senators to ensure that Mueller and his investigation are protected.

Why hasn’t that already happened? In April, Senate Majority Leader Mitch McConnell ruled out the possibility of the Special Counsel Independence and Integrity Act, or any other legislation protecting the special counsel, from getting to the Senate floor. “There’s no indication that Mueller’s going to be fired,” McConnell told Fox’s Neil Cavuto.

But in the months since, Trump and his supporters have grown increasingly hostile to Mueller, the FBI and the Justice Department. That hostility included the especially disquieting release of a memo that House Republicans wrongly said showed bias in the origin of Mueller’s investigation.

Senators have meekly and quietly watched this denigration of Mueller and the nation’s law enforcement agency. Now Mueller’s fiercest protector may leave, and the nation might be one step closer to a potential constitutional crisis.

It’s time for Tillis and Graham to revive their bill and renew their call for it to heard on the Senate floor.