But Trump's most talkative attorney thinks a president, unlike the rest of us, can't be successfully subpoenaed.
“[I]t’s pretty clear that a president can’t be subpoenaed to a criminal proceeding about him,” said Rudolph W. Giuliani in an interview last week with Fox News's Sean Hannity.
Legal experts say both sides are stepping out in front of the facts by making claims about a presidential subpoena. This sort of thing has never been done before, which means that we don't know how the courts would rule when a president is pitted against an independent investigation with ties to the president.
But the nation may be coming up on such a historic legal battle. Trump looks increasingly as though he will refuse a face-to-face interview with Mueller on all things Russia, which would mean he would rather risk a protracted court fight than voluntarily testify under oath. He might win such a court fight and get out of talking to Mueller entirely.
Here's what Trump and his attorneys are likely gaming out right now about whether the subpoena risk is worth taking:
Why Mueller might not be successful in subpoenaing Trump
Jack Sharman, who was a special counsel to Congress during the Whitewater investigation into the Clintons' real estate investments, thinks Mueller's subpoena request is really more of a negotiating tactic than an actual threat. Mueller probably knows full well that it's unclear whether the courts will agree to force a sitting president to do such an interview — just as it's murky on whether a sitting president can be indicted.
It comes down to whether the judicial branch agrees that forcing Trump to be interviewed would constitute interference in the executive branch. Doesn't the president have a right to say no to protect not just himself but the office he represents?
“I would think a court would be hesitant to insert themselves in the middle of that,” Sharman told The Fix last week.
A court did force President Richard M. Nixon to hand over tapes in the Watergate investigation, but that was different, Sharman said. The court was dealing with evidence, not the person charged with running the country. A couple of decades later, independent counsel Kenneth Starr issued a subpoena to President Bill Clinton in the Monica Lewinsky case. But Starr retracted that as the two came to an agreement on the president being interviewed. So the courts never got involved.
The Starr playbook could be exactly what Mueller is following here, Sharman said. Reading between the lines of a subpoena threat, Mueller might be saying something like this: “I may not ultimately win the legal battle, but it will be so difficult for you that why don't we agree to some other resolution, like a voluntary interview?”
A court also would likely consider what a subpoena would mean for Trump — that, instead of voluntarily sitting down with Mueller with the president's legal team by his side, a subpoenaed Trump would be forced to appear before a grand jury, his lawyer nowhere in sight.
“That scenario would strike many as inappropriate for the dignity of the office,” Sharman said, and he theorized it could make any court that is hesitant of appearing to overreach its powers disinclined to force Mueller's subpoena.
Why Mueller might successfully subpoena Trump
Remember how Nixon's tapes were successfully subpoenaed? A constitutional expert told The Washington Post's Philip Bump that the Supreme Court at the time said Nixon, himself, could be subpoenaed.
“Neither the doctrine of separation of powers nor the generalized need for confidentiality of high-level communications, without more, can sustain an absolute, unqualified Presidential privilege of immunity from judicial process,” read the 1974 decision in United States v. Nixon.
Of course, that was Nixon, not Trump, and it was in theory, not practice.
But as Louis Seidman, a professor of constitutional law at Georgetown University, told Bump, "There is nothing in the Constitution that says or implies that ‘a president cannot be distracted by a criminal investigation.' ”
In other words: Trump could become the first sitting president to be forced to be interviewed in an investigation. Or he might not. The question facing Trump is whether he wants to risk the possibility of losing a subpoena fight to get out of a voluntary interview with Mueller.