WASHINGTON — It’s been more than six months since President Donald Trump claimed to have started his annual physical at Walter Reed hospital but the White House is declining to explain why he has yet to complete the yearly doctor’s examination.

Senior administration officials did not immediately respond to NBC News’ request for comment about the delay — despite Trump announcing this week he was taking an unproven and potentially dangerous drug after being exposed to an aide who tested positive for coronavirus.

Asked in early March about when he would complete his physical, the president told reporters, “I’m going probably over the next 90 days. I’m so busy, I can’t do it.”

A month later, as the coronavirus pandemic hospitalized UK Prime Minister Boris Johnson, Trump said he would finish the exam “at the appropriate time” adding, “but I feel very good.”

A president’s annual physical typically occurs at the beginning of a new year. Trump’s 2019 exam was conducted in February, and his 2018 physical was conducted in January. It is uncommon for a president to complete a routine physical exam months apart and in multiple stages.

“As a part of granting a president as much power as we do, he has the obligation to demonstrate that he is well or, if he is not, to let us know exactly what is amiss,” said presidential historian Michael Beschloss.

“From the time in the 1950s when Dwight Eisenhower released unprecedented information about the heart attack, ileitis and stroke he suffered in office, most presidents have fulfilled that demand, including releasing the results of regular physicals,” Beschloss said. “Too often in history have presidents concealed secret illnesses and medicine routines that had the potential to undermine their leadership, and the wellbeing of all of us.”

In November 2019 — six months ago this week — Trump began what the White House described as “portions” of his third physical during a two-hour examination at Walter Reed National Military Medical Center.

That visit to Walter Reed was unannounced and remained shrouded in secrecy for two days as the president remained out of public view and as the White House declined to answer questions about it.

The president’s physician, Dr. Sean Conley, later wrote in a memo released by the White House that Trump’s “interim checkup” had been “routine.” Conley at the time said a “more comprehensive” examination would occur this year and that the president’s labs and exam results would be released in a corresponding report.

At 73, Trump is the oldest person to be sworn in for his first term as president.

Questions about Trump’s health are newly relevant, given his announcement this week that he is taking hydroxychloroquine to ward against contracting the coronavirus. The president described it as a “two-week regimen,” which ends today. Trump has repeatedly promoted the anti-malarial drug as a coronavirus treatment despite multiple warnings about its dangers.

The Lancet medical journal on Friday published the results of a large observational study, which found that hydroxychloroquine use is linked to increased rates of mortality and heart arrhythmias among hospital patients with COVID-19.

Trump — in a previous physical conducted in 2018 — had been diagnosed with a form of heart disease common among men in his age group.

The president — whom the White House says is tested daily for the virus — said Conley “didn’t recommend” hydroxychloroquine but offered it to him.

Conley replaced Rear Adm. Ronny Jackson, who left the job in a failed nomination to serve as secretary of Veteran Affairs.

Two sources with direct knowledge tell NBC News that Jackson handpicked Conley as his successor and that Conley is viewed by many within the White House Medical Unit as being unfairly promoted to the job of physician to the president without proper vetting. Neither the White House nor Jackson responded to a request for comment.

When pressed on the findings of The Lancet study during a Friday White House press briefing, the administration’s coronavirus task force response coordinator, Dr. Deborah Birx, dodged a specific question on what the new review may mean for the president’s health.

Birx cited ongoing, controlled trials for the drug, but made clear those results are “still pending” and urged Americans to focus on the comorbidities which would make hydroxychloroquine more dangerous, such as heart disease and obsesity.

“You can see dramatically the increased risk for that,” she said, without referencing Trump.