Sen. Bernie Sanders (I-Vt.) campaigns at Dartmouth College in Hanover, N.H., last month. (Cheryl Senter/AP)
Opinion writer

The Post reports: “Democratic presidential candidate Bernie Sanders underwent a heart procedure after experiencing chest discomfort at an event, a campaign official said Wednesday, prompting him to cancel his upcoming schedule as he recovers.” He is reportedly “conversing and in good spirits.” The campaign “declined to immediately provide more details about Sanders’s condition or to disclose where he was on Wednesday, pointing to [Sanders senior adviser Jeff] Weaver’s statement when asked by a reporter about his whereabouts.” He will be resting for “a few days.”

We certainly hope Sanders, who is extremely fit and active, is back on the trail soon. However, the campaign’s initial response, offering as few details as possible, is unacceptable. It behooves them to be more forthcoming and to explain, for example, why the campaign “abruptly decided to put off plans for a $1.3 million investment to air the ad in Iowa on Wednesday,” as The Post reported.

And yes, it is time to raise questions about age and fitness with regard to all candidates, but especially with regard to the top three. If elected, former vice president Joe Biden would be 78, Sanders 79 and Sen. Elizabeth Warren 71 on Inauguration Day; each one — Biden, Sanders or Warren — would be the oldest elected president at the start of his or her presidency.

There has been a lot of chatter about Trump’s verbal acuity and mental state, but the issue is not him per se or Sanders or any other individual contender. The presidential campaign is stressful and exhausting, the presidency more so. Rather than pick out any single candidate, it would be advisable for them all to stick to some basic rules.

First, when an incident is so serious as to require hospitalization, the campaign should answer any and all questions from the press. The candidate also should authorize his or her doctor to answer all questions as well.

Second, candidates should release his or her medical files (not simply a signed doctor’s letter of the kind Trump produced) well in advance of the first primary. Sure, it is a substantial invasion of privacy, but no one forces these candidates to run for president. The voters have every reason to demand all the data they need to evaluate candidates’ physical health.

Third, candidates would be wise to agree in advance to annual physical and mental fitness exams if elected, and to release as much data as possible. It would be advisable to impanel some independent experts to agree upon what data is important and what tests should be run. We would do well to have clear, objective criteria that apply across the board regardless of who is president.

Trump should, of course, agree to this as well. If reelected, he’ll be about 74½ on Inauguration Day. We already know he does not exercise and is overweight. It is perfectly legitimate to insist the same rules apply to him as to potential competitors.

This isn’t ageist. In fact, older candidates especially should want these kinds of rules in place if only to give the voters comfort that they are physically up for the job. It also is good insurance against the kind of rumor-mongering and conspiracy theories spread by Trumpers about Hillary Clinton’s health in 2016. And don’t think Trump won’t do it again in 2020 should he be on the ballot.

Read more:

David Byler: Biden’s age is a real issue. That doesn’t mean it’s easy to talk about.

Greg Sargent: Be very afraid. We’re missing something big about Biden’s age.

Helaine Olen: Why don’t voters care if a presidential candidate is old?

Evan Thomas: How old is too old to be president?

Jeffrey Sonnenfeld: Think Biden and Trump are too old for the White House? Take a look around.

Jennifer Rubin: Old men have an electability problem