Former Federal Bureau of Investigation Director Robert Mueller, appointed as a special prosecutor in the inquiry into possibly tampering with the 2016 presidential election process in May, left his position at the FBI after a farewell party at the Justice Department in Washington, D.C., on August 1, 2013. Reuters

The Washington, D.C., grapevine said Donald Trump would fire Special Counsel Robert Mueller, the former Federal Bureau of Investigation director selected in mid-May to lead the Justice Department probe of alleged Russian meddling in the 2016 election. Then the rumor mill said he wouldn’t. But if President Trump or his attorney general, Jeff Sessions, wanted to eliminate Mueller, they could: The law that would’ve stopped them has expired.

Originally a measure of the 1978 Ethics in Government Act, a reform law meant to target the sort of behavior at the heart of the Watergate scandal, the Independent Counsel Act, passed a decade later, established the process by which the Justice Department can hand off investigations to a special prosecutor to avoid conflicts of interest. The Act made it difficult for the attorney general to fire that special counsel. It expired in June of 1999.

Read: Donald Trump May Fire Robert Mueller, Russia Collusion Investigator, Citing Conflict Of Interest

Congress’ decision not to renew the law followed the independent counsel investigations of then-President Bill Clinton’s conduct by the widely-criticized former Solicitor General Kenneth Starr and several other special prosecutors, which collectively cost nearly $80 million.

The Independent Counsel Act traces its origins to the infamous “Saturday Night Massacre.” It fell victim to criticism related to wasteful spending, but served as a mainstay of judicial independence for its short lifetime, said Georgetown Law School professor Laura Donohue.

“The risk is, the president might just keep firing people until someone’s not investigating properly. And it doesn’t even have to be Trump. It could be anyone, any president,” she said. “Nixon kept firing everyone who was investigating him.”

Current law — namely, Title 28, Chapter 6, Part 600, Section 7 of the Code of Federal Regulations — states that the attorney general reserves the right to remove or discipline a special counsel “for misconduct, dereliction of duty, incapacity, conflict of interest or for other good cause, including violation of Departmental policies.”

That part of the Code of Federal Regulations, according to Harvard Law School professor Alan Dershowitz, “is an area of law that is very uncertain.”

“There’s no question in my mind that the Ethics in Government Act made it far more difficult to fire special prosecutors,” said Dershowitz, who is writing his own article on the subject. Under Constitutional law, Dershowitz said, Trump “can do anything that Sessions can do [because] the way our Constitution is set up, the executive branch is the president.”

Congress could pass a replacement for the expired Independent Counsel Act, Dershowitz said, but official passage of the law would require the president’s signature.

Read: Special Counsel Robert Mueller Could Object To James Comey's Public Testimony Before Intelligence Committee

Rumors of Mueller’s possible removal swirled after CNBC Washington correspondent Kayla Tausche tweeted that she’d seen Chris Ruddy, CEO of the far-right outlet Newsmax, leave the White House’s West Wing.

An hour later, Ruddy appeared on PBS Newshour, telling host Judy Woodruff that he believes Trump is “considering perhaps terminating the special counsel.”

“I think he’s weighing that option,” Ruddy said. “I think it’s pretty clear by what one of his lawyers said on television recently.”

Although American Urban Radio Networks White House Correspondent April Ryan told CNN’s Erin Burnett of “mass hysteria in the West Wing about this” later that evening, Deputy Attorney General Rod Rosenstein told senators during a hearing Tuesday that there was “no secret plan” underway to remove Mueller. Around the time of the hearing, Philip Rucker, the Washington Post’s Washington, D.C., bureau chief, tweeted that Ruddy had informed him that White House Press Secretary Sean Spicer called the Newsmax CEO “asking him to issue a statement saying he didn’t talk to Trump about Mueller.”

Either way, as Rep. Adam Schiff (D-Calif.) noted, the president could face a stern reaction from Congress if he tried to get Mueller out of the picture.