What should the special counsel do next? I’d suggest it’s subpoena time.

Robert S. Mueller III has proved himself a remarkably patient prosecutor. His negotiations with President Trump’s lawyers have stretched on for at least six months of slow-walking and subject-narrowing. And Mueller has stayed silent, as a responsible prosecutor should, while Trump bad-mouthed his investigation as a rigged “witch hunt” and demeaned his team as being led by “13 very Angry and Conflicted Democrats.”

But the clock is ticking on the investigation. Trump’s latest lawyer, Rudolph W. Giuliani, has been on television asserting that the president dearly wants to testify but can’t be trusted to do so. (“This is the reason you don’t let the president testify,” Giuliani said on ABC’s “This Week,” by way of explaining shifting accounts about Trump’s involvement in misleading the public about his son’s meeting with a Russian lawyer.)

In any event, Giuliani added, he’d need all sorts of other assurances before making his client available. “There’s got to be a high bar they have to reach in terms of convincing us that they’re fair, convincing us that we’re going to get the things we need,” he said. “I want to see the ‘Spygate’ report, haven’t gotten it. I want to see the authorization that they have, which they gave to [U.S. District Judge T.S. Ellis III, who is overseeing one of the cases against former Trump campaign chairman Paul Manafort] . . . but Judge Ellis hasn’t written an opinion yet, which convinces me there’s a real problem with it.”

Somehow I doubt that former U.S. attorney Giuliani would have appreciated this sort of highhandedness from the subjects of his criminal investigations. And somehow, I think Mueller may be getting the message: Absent a subpoena, and maybe even with one, Trump isn’t answering his questions. In case there was any mystery about that, Giuliani all but said so: “We’re leaning toward not,” he told George Stephanopoulos.

Certainly, a president isn’t an ordinary witness; the demands of office mean that he deserves a significant degree of accommodation. And certainly, Trump’s lawyers aren’t the first to use an arsenal of delaying tactics to put off a special counsel. The Bill Clinton impeachment documents reveal a months-long minuet between Clinton attorney David Kendall and the office of independent counsel Kenneth W. Starr as they jockeyed over whether Clinton would testify.

In the end, the grand jury issued a subpoena for Clinton’s testimony. That order was withdrawn when Clinton’s lawyers agreed to allow him to testify — at the White House; with his lawyers present, not the ordinary arrangement when appearing before a grand jury; and for a limited time (four hours).

So as push comes pretty close to shove, Mueller faces a choice. He could decide that a subpoena, and the ensuing litigation with Trump, wouldn’t be worth the cost in disruption and delay. Team Trump’s bravado notwithstanding, Mueller would be likely to win any constitutional showdown over his authority to enforce a subpoena of the president.

“It’s pretty clear that a president can’t be subpoenaed to a criminal proceeding about him,” Giuliani told Sean Hannity last month. Really? Ask Richard Nixon, and the justices who ruled unanimously that he had to turn over the tapes. Ask Clinton, and the justices who ruled unanimously that he had to testify in Paula Jones’s civil lawsuit. The law is not absolutely clear, but it is overwhelmingly on Mueller’s side, if he chooses to press a subpoena.

But sorting that out could take months, if not longer, and a special counsel faces time pressures different from those confronted by an ordinary prosecutor. And to what end? If the subpoena is eventually upheld, Trump could assert his right against self-incrimination to avoid testifying, especially as to the matters of most intense interest to Mueller. Department practice is not to subpoena targets of an investigation, but Mueller has reportedly told Trump he is not a target. And even if Trump were to testify, how much valuable information could prosecutors really extract from him?

On the other side of the ledger, tough prosecutors don’t make it a habit to back down in the face of recalcitrant witnesses; Mueller is nothing if not a tough prosecutor, unlikely to simply say “never mind” after months of seeking Trump’s testimony. And as much as Mueller has an interest in both pursuing and concluding the Russia probe, he also has an obligation to history and to be mindful of the precedents that are being set.

Backing down in the face of presidential recalcitrance would not only reward Trump but also tell future presidents that they can evade the ordinary demands of the law as long as they have the stomach to bully and delay. Mueller shouldn’t let that happen. He has waited long enough.

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Read more:

Ruth Marcus: The Trump team’s chilling message to Mueller

Jennifer Rubin: Word salads, contradictions and hints of authoritarian delusion

Greg Sargent: Secret memo to Mueller actually reveals weakness of Trump’s position

The Post’s View: One year of Robert Mueller

Quinta Jurecic: Trump is tightening his grip around the neck of the Justice Department