WASHINGTON (AP) — A new book is reviving questions about President Donald Trump's unscheduled visit to Walter Reed military hospital last fall with the revelation that "word went out" for Vice President Mike Pence to stand by to temporarily assume presidential powers if Trump had to receive anesthesia for a medical procedure.

The White House has said the president's November 2019 visit, which raised questions at the time about Trump's health, was part of his routine annual physical, and said the president wanted to get a head start on what typically is an hours-long, head-to-toe exam because he'd be busy this year with campaigning.

A president's routine medical checkup typically is announced ahead of time.

The White House provided no other details at the time. Trump's White House doctor said in a statement Tuesday the president "remains healthy" and "fit to execute the duties of the Presidency." Pence's office declined comment.

Trump visited Walter Reed National Military Medical Center in Bethesda, Maryland, about a month before the Democratic-controlled House impeached him over his conduct toward Ukraine.

"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," Michael Schmidt writes in "Donald Trump v. the United States: Inside the Struggle To Stop A President."

"Pence never assumed the powers of the presidency, and the reason for Trump's trip to the doctor remains a mystery," Schmidt says in the book. Schmidt is a New York Times and Pulitzer Prize-winning reporter.

Trump responded Tuesday on Twitter to Schmidt's reporting and other speculation about his health, and later had his White House doctor attest to his health.

"It never ends! Now they are trying to say that your favorite President, me, went to Walter Reed Medical Center, having suffered a series of mini-strokes. Never happened to THIS candidate - FAKE NEWS," Trump tweeted.

Trump, 74, appeared to be responding to Clinton White House veteran Joe Lockhart, who tweeted Monday about Trump, asking, "Did @realDonaldTrump have a stroke which he is hiding from the American public?"

Dr. Sean Conley, Trump's White House doctor, followed up Tuesday with a statement in which he said Trump has not experienced or been evaluated for a stroke, a mini-stroke or any acute cardiovascular emergency.

"The president remains healthy and I have no concerns about his ability to maintain the rigorous schedule ahead of him," said Conley, who flew with Trump to Wisconsin on Tuesday. "As stated in my last report, I expect him to remain fit to execute the duties of the presidency."

In June, Conley released a statement saying Trump had completed the physical in April. Along with releasing some findings about the president's health, Conley said there were "no findings of significance or changes" and said Trump "remains healthy."