Update: On Tuesday, The Post reported that special counsel Robert Mueller raised the possibility of subpoenaing President Trump during a meeting in March. In February, when the possibility was being discussed, we spoke with legal experts who explained what the repercussions of such a move would be — and how Trump would likely respond.

As a rule, defense attorneys aren’t eager to have their clients speak with law enforcement. There’s very little upside and a huge downside in the best of scenarios. Testifying under oath immediately means that you’re risking perjury charges; talking to authorities at all means (as the Miranda saying goes) that your words can be used against you.

And that’s for a normal person. When you scale this scenario up to the president of the United States and his interlocutor to a person specifically assigned his position to uncover wrongdoing on the president’s part, the stakes are incalculably high. So it’s no surprise that President Trump’s lawyers aren’t champing at the bit to have him provide testimony to special counsel Robert S. Mueller III. If Mueller wants to find out what Trump knows, he may have to do something that has  been rare in U.S. history: subpoena a sitting president.

For a layperson, being served with a subpoena to testify largely ties your hands. You can reject or ignore it, but then you face contempt of court charges and possible prison time. For Trump, the question takes on a number of other unique dimensions — and the consequences of a refusal to respect a subpoena could lead to nothing short of a question about the nature of America itself.

But we’ve gotten ahead of ourselves. Let’s build up to that by considering the steps that might unfold beginning at the moment Mueller decides he wants to hear Trump’s testimony.

I spoke with two constitutional law experts, Lisa Kern Griffin, professor of law at Duke University, and Louis Seidman, Carmack Waterhouse professor of constitutional law at Georgetown University.

Step 1: Mueller decides to hear from Trump

It’s not a foregone conclusion that Mueller will seek testimony from Trump — at least right now. As will become very clear shortly, reluctance by the president to comply with Mueller could lead to a significant legal fight, which doesn’t necessarily do Mueller much good over the short term.

“There are reasons why he might not want to get into a power struggle with the White House,” Griffin said. “It will prolong and delay his investigation,” and litigation “may not be the most productive thing for him to be focused on at this juncture in his investigation.”

It has been reported that Mueller and Trump’s attorneys may be trying to find a middle ground, reaching a consensus on ways in which Trump could provide answers to Mueller’s questions short of live testimony in front of a grand jury. When Bill Clinton was deposed in a sexual harassment lawsuit in 1998, it took place at his attorneys’ office in Washington. The ground rules, methodology and time constraints are subject to negotiation and bounded largely by whatever Mueller feels is appropriate.

But again: Any testimony at all could be problematic for Trump. (Particularly given his track record in depositions.) If Trump’s attorneys can’t negotiate a way to testify that satisfies their concerns and to which Mueller will agree, and if Mueller decides that he wants to press the issue, he can issue a subpoena.

Step 2: Trump doesn’t short-circuit the process

Before we get to the question at hand, there’s an important subject to consider.

Mueller serves at the pleasure of Deputy Attorney General Rod J. Rosenstein who, last May, appointed the former FBI director as special counsel. (Attorney General Jeff Sessions had recused himself in March because of his involvement in the Trump campaign.) For Mueller to take significant steps in his investigation, Rosenstein needs to sign off — including, Seidman told me, issuing a subpoena to the president.

You can see the problem here. If Rosenstein were suddenly sympathetic to Trump, he could decline to issue the subpoena. Or, if Trump wanted to, he could simply replace Rosenstein with someone who was sympathetic to the president’s concerns.

Trump can’t fire Mueller directly, but he can fire Rosenstein and in recent days has declined to deny that he might do so. If Trump fires Rosenstein, authority over Mueller gets kicked down the chain of command at the Justice Department — unless Trump replaces Rosenstein quickly. Rosenstein was appointed by Trump last year and confirmed by the Senate, but according to the Vacancies Reform Act of 1998, Trump could potentially fill the deputy attorney general spot with any other already-confirmed appointee he wishes. (Whether the VRA applies if the vacancy is created through someone being fired is unclear.)

The example that Seidman used was moving EPA Administrator Scott Pruitt over to serve as DAG.

“You would slide somebody over, and that person would then say, ‘You can’t subpoena the president, and, what’s more, you can’t investigate his financial holdings,’ ” Seidman said. “Just a whole bunch of limitations.”

Mueller would effectively be neutered, and the question that would then arise is whether Mueller would resign — and, if he did, what would happen next.

But that’s a different theoretical. Let’s assume that Trump doesn’t take this step, that Mueller remains able to issue a subpoena and that Rosenstein remains able to approve it. It gets to the White House.

Step 3: Trump decides to fight the subpoena

This is where the Supreme Court would probably need to get involved.

“If the president does not respond to the subpoena or moves to quash the subpoena,” Griffin said, “there will be litigation in court about the constitutionality of subpoenaing a sitting president. That litigation will probably be governed by the Nixon case, which was functionally about the same issue, although it was tapes and not testimony that was in play.”

The “Nixon case” to which she refers is United States v. Nixon. In 1974, the White House was subpoenaed for tape recordings and documentation of meetings between then-president Richard M. Nixon and individuals who had already been indicted by a grand jury. Nixon partially complied but fought the full release of the material. The Supreme Court ultimately ruled unanimously that Nixon and the White House had to turn over the subpoenaed records. About two weeks later, Nixon resigned.

“Typically the law is that, before you can contest a subpoena you have to go to contempt,” Seidman said. “If Trump were an ordinary person, he couldn’t just appeal the subpoena. He would have to refuse to comply, be held in contempt and then appeal the contempt citation. But in the Nixon case, the court made an exception and it allowed an appeal without Nixon actually going to contempt.”

Should the Trump White House decline to provide Trump’s testimony, then, his attorneys would probably quickly find themselves arguing their case before the country’s highest court.

What would their argument be?

“Trump will make a bunch of legal arguments, who knows what they are, but I could imagine him saying that the special counsel is illegal, that he’s exceeded his jurisdiction, that under Clinton v. Jones the president is entitled to a certain accommodations that he’s refused to grant,” Seidman said. “He’ll just make something up, and so then it will go to court.”

Where the court would land in that fight isn’t entirely clear, but both Seidman and Griffin said they assumed that Trump would lose.

“I think that the precedent set by the Nixon case is unfavorable to the president’s claim that he is somehow above the law and cannot have his testimony compelled before the grand jury,” Griffin said. She noted that Trump does have the Fifth Amendment protection against self-incrimination — but that is politically problematic.

Step 4: Trump decides to ignore the court

At this point, Trump will have been instructed to provide testimony to Mueller’s team. This could mean that his attorneys work with Mueller to figure out how and when that happens. Or it could mean that Trump simply ignores the court’s decision.

What then?

“Then it becomes a standoff between the court’s authority and the authority of the White House and the executive branch,” Griffin said, “because the court will be functionally issuing an order that the president has to appear and answer questions.”

“At that point,” Seidman said, “what would have to happen is that some court would have to hold the president in either civil or criminal contempt. There is no case law about that. No president has ever been held in contempt. Nobody’s ever tried to hold a president in contempt, and it’s anybody’s guess what a court would say about that.

“One of the means of enforcing a contempt judgment — either civil or criminal — is to incarcerate the person,” he continued. “In a case of civil contempt, it’s until the person relents. For criminal contempt, a sentence is imposed. In either event, the president would be locked up, and nobody thinks that’s plausible.

“The other alternative for civil contempt would be a fine that he would have to pay every day,” Seidman  said. “At this point, this gets pretty ridiculous, right? I mean, the president — maybe doesn’t have as much money as he claims, but he has a lot of money, and I don’t know that that would be very effective or very seemly.”

That bizarre scenario, though, obscures the bigger issue.

“The specter of someone hauling him into court is exaggerated,” Griffin said of Trump. “But if he refuses to accommodate the special counsel’s questions in any way, shape or form, then there will be a constitutional crisis. There will be literally a debate between two branches of our government as to whose authority is paramount, and that is unprecedented.”

Perhaps at that point Trump is impeached by Republicans in Congress. Perhaps, though, the issue is unresolved, and Trump holds out.

Were the situation not to be resolved, Seidman said, “we would wake up the next morning or a week later in a very different country than the country we live in now.”

Or maybe Trump would simply reach an agreement to answer Mueller’s questions. We’ll just have to wait and see.