WASHINGTON — If Robert Mueller seeks to question President Donald Trump, could the White House successfully refuse to make him available?

Like anyone whose testimony is sought by grand jury subpoena in a criminal case, the president could cite his Fifth Amendment right not to testify against himself. Such a move, however, would carry significant political risk.

Related: Talks underway about Trump interview in Mueller Russia probe

The White House has given no indication that the president would refuse to answer Mueller's questions. Trump said in June that he was "100 percent" willing to give Mueller his version of events. "I'd be glad to," the president said when asked at a news conference.

But suppose he changed his mind. Could he decline to respond to a subpoena from Mueller on some other grounds? The answer, in a word, seems to be no.

The Supreme Court has never directly addressed the question about whether a president can refuse to cooperate in a criminal investigation potentially involving his own conduct. That's because no president has ever fought such a request. But in two other cases, the court has suggested that there's no authority to decline.

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President Richard Nixon failed when he tried to shield his White House tapes from the Watergate prosecutor who wanted them as evidence in charging presidential aides with crimes related to the scandal. The court rejected Nixon's claim that the recordings were protected by executive privilege.

"The President's generalized assertion of privilege must yield to the demonstrated, specific need for evidence in a pending criminal trial and the fundamental demands of due process of law in the fair administration of criminal justice," the court said in 1974.

Twenty-three years later, the Supreme Court ruled that President Bill Clinton was not immune from a lawsuit filed by Paula Jones, who accused him of sexual harassment.

It's settled law, the court said, "that the President is subject to judicial process in appropriate circumstances."

While that ruling involved a private civil case, the court said the need for evidence in a prosecution is even greater.

"We have made clear that in a criminal case the powerful interest in the 'fair administration of criminal justice' requires that the evidence be given under appropriate circumstances lest the 'very integrity of the judicial system' be eroded."

Two former White House counsels, under Republican and Democratic presidents, agreed Trump would have no legal grounds, other than the Fifth Amendment, to reject a subpoena for his testimony. Both spoke on condition that they not be identified.

Clinton became the first sitting president ever questioned by prosecutors about his own conduct. In 1998 Kenneth Starr's team asked him about his relationship with White House intern Monica Lewinsky for nearly six hours in the Map Room, as a grand jury watched on a special video feed to the federal courthouse 10 blocks away.

Starr's team had earlier interviewed both the president and Hillary Clinton in 1995 about the Whitewater real estate matter, and they gave sworn testimony about Whitewater the year before to Robert Fiske, the special counsel who was initially appointed to investigate the issue.

Previous presidents have cooperated in criminal investigations while in office. Ronald Reagan answered written questions from the special counsel investigating the Iran-Contra scandal. Jimmy Carter gave four depositions in criminal cases unrelated to his own conduct. And Gerald Ford gave a videotaped deposition in the trial of a woman accused of trying to assassinate him.

A century earlier, President Ulysses Grant gave a long deposition in a criminal case, testifying for the defense in the Whiskey Ring scandal.

While it's unlikely Trump could successfully refuse to answer Mueller's questions if subpoenaed, how he does so would probably be negotiated. The special prosecutor might not be able to force him to appear on videotape for a deposition and might have to settle for written answers.

Mueller could try to summon the president to appear in court, though his lawyers could cite the Clinton precedent and seek to have the questioning done in the White House. In its ruling in the Clinton civil case, the Supreme Court said, "We assume that the testimony of the President, both for discovery and for use at trial, may be taken at the White House." But that was a civil case with no grand jury.