Shortly before 3 p.m. on Nov. 16, President Trump arrived at Walter Reed National Military Medical Center in Bethesda, Md. The White House pool reporter on duty described the president as leaving the White House a half-hour earlier, “wearing a long dark overcoat and carrying what looked like a tan rectangle-shaped folder or envelope under his arm.” Until the presidential motorcade arrived at the hospital, though, news of Trump’s departure wasn’t reportable.

And with that, a mystery was born.

Trump was there for about two hours, arriving at 2:47 p.m. and leaving at 5:03 p.m.

When the president arrived, his press secretary, Stephanie Grisham, told reporters that Trump was “taking advantage of a free weekend” to “begin portions of his routine annual physical exam.” After Trump left the facility, Grisham offered more details.

“After a quick exam and labs, the president is headed back downtown,” she said in a statement, noting that Trump remained healthy “as demonstrated by his repeated vigorous rally performances.” While at the facility, Grisham said, Trump greeted the staff and met with the family of a soldier wounded in Afghanistan.

Each week, the White House sends out photos from the president’s prior seven days. The following week, no photos of these encounters were provided, though Trump did tweet about it.

That this stop at Walter Reed happened without prior announcement was unusual. He’s gone twice this year on business that wasn’t health-related; both times, the trips were included in his public schedule. When he went for his checkup in February last year, it was similarly included on his public schedule. Those times, he also traveled to the facility via Marine One. In November, he traveled by motorcade.

All of this fueled the mystery. Why the unannounced trip? Was it just a “free weekend?” (The previous weekend, he was at Trump Tower in Manhattan and the following weekend at Mar-a-Lago in Florida.) Or was there something more dramatic at play?

Over the next few days, Trump joked about the incident, disparaging the media’s curiosity.

“I went for a physical on Saturday,” he said at a Cabinet meeting on the following Tuesday. “My wife said, ‘Oh, darling, that’s wonderful.’ Because I had some extra time. Because it looks like January could be a busy month” — because of the impending Senate impeachment trial.

“I came back, my wife said, ‘Darling, are you okay?’ ” Trump continued. “ ‘What’s wrong?’ ‘Oh, they’re reporting you may have had a heart attack.’ I said, ‘Why did I have a heart attack?’ ‘Because you went to Walter Reed Medical Center.’ ” He later claimed that CNN had reported he “had massive chest pains."

“I went — did a very routine — just a piece of it,” Trump said; “the rest of it takes place in January — did a very routine physical."

He did not go back for the second part of his physical. There was no report released after his November visit, as there had been the preceding February. In June, Trump’s team did produce a memo memorializing the president’s health, including an assertion that the president had completed his physical at the White House. That report came at a useful time, politically: Trump’s halting walk down a ramp at the U.S. Military Academy at West Point earlier in the month raised questions about his health and fortitude. (Trump is the oldest person to be elected as president.)

All a bit murky, but a mystery that eventually faded. Until Tuesday, when a book from New York Times reporter Michael Schmidt was published. It includes an interesting new detail about Trump’s trip to the hospital:

“In reporting for this book, I learned that in the hours leading up to Trump’s trip to the hospital, word went out in the West Wing for the vice president to be on standby to take over the powers of the presidency temporarily if Trump had to undergo a procedure that would have required him to be anesthetized. Pence never assumed the powers of the presidency, and the reason for Trump’s trip to the doctor remains a mystery.”

In an interview with Fox News’s Bret Baier on Tuesday, Vice President Pence said he didn’t “recall being told to be on standby.”

It’s not unheard of for the vice president to be prepared to assume the duties of the presidency while the chief executive undergoes a medical procedure. George H.W. Bush was briefly acting president in July 1985 as Ronald Reagan — the oldest person to hold the position — had surgery. But there was a big difference: The Reagan surgery was planned and telegraphed to congressional leaders in advance in accordance with the provisions of the Constitution’s 25th Amendment. Trump’s wasn’t, emerging only when reported by Schmidt.

That such a step was considered, implying that Trump would be incapacitated, implies that something more dramatic was afoot than a simple annual physical. What, though, remains unclear.

On Tuesday, Trump poured some accelerant on the story, with an out-of-left-field tweet on the subject.

This claim about “mini-strokes” was apparently spurred by author Don Winslow, who made the allegation in a tweet of his own. It was accompanied by a video showing Trump speaking with some difficulty in December 2017.

In short order, the White House released a statement from Trump’s physician, Sean Conley, bolstering the president’s denial.

“I can confirm that President Trump has not experienced nor been evaluated for a cerebrovascular accident (stroke), transient ischemic attack (mini stroke), or any acute cardiovascular emergencies, as have been incorrectly reported in the media,” Conley said. “The president remains healthy, and I have no concerns about his ability to maintain the rigorous schedule ahead of him. As stated in my last report, I expect him to remain fit to execute the duties of the presidency.”

Unfortunately for Trump, his track record with statements from physicians isn’t that great. During the 2016 presidential election campaign, his physician, Harold Bornstein, offered a glowing appraisal of Trump’s health — an appraisal that he later admitted Trump’s staff had written. In 2018, Trump’s doctor, Ronny L. Jackson, was nearly as effusive, including an aside about Trump’s “incredible genes.”

An additional challenge for the president is that he has, for two presidential election cycles, attempted to cast his opponents as enfeebled or unhealthy. For months, he and his allies disparaged Democratic presidential candidate Joe Biden as mentally unfit, criticisms that faded somewhat after Biden was nominated at the Democratic convention. Four years ago, Trump and his supporters repeatedly attempted to raise questions about the health of Democratic presidential nominee Hillary Clinton.

One of the voices that helped boost the “Clinton isn’t well” narrative was Matt Drudge, who runs a popular political website. Over the course of Trump’s presidency, though, Drudge has become increasingly critical of the president, as made obvious in the stories he chooses to promote.

On Tuesday, he turned his spotlight on Trump’s physical health.

It seems safe to say that not everyone is persuaded that November’s trip was a nonissue.

This article was updated with Pence’s comments to Baier.