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It may be one of the biggest—and most significant—broken promises of the Democratic 2020 race. In October, a month after he suffered a heart attack and had two stents inserted, Sen. Bernie Sanders told Dr. Sanjay Gupta of CNN that he would release his medical records. No ifs, ands, or buts, Sanders stated, “The people do have a right to know about the health of a senator, somebody who’s running for president of the United States—full disclosure.”

Sanders has not kept that vow. He has not made public his medical records. And he has not released one crucial piece of information that would let voters know how his heart is doing.

In December, the 78-year-old Sanders did share with the public letters from three doctors who attested that he was in good health and fit to campaign and serve as president. But these were not compete records—two of the three letters were each one paragraph long. And none of the letters included a key measurement of his heart’s performance: the left ventricular ejection fraction. This standard rating shows how much blood the heart pushes out with every beat.

I recently met a biomedical engineer who specializes in coronary matters, and he told me this one indicator would show just how well Sanders’ heart is functioning. “It’s really most of what you’d want to know,” he said. And recently, the president of the American College of Cardiology, Richard Kovacs, told NBC News that if Sanders released this measurement, it would likely address any lingering questions and indicate if the heart was pumping out the normal 60 percent—or less. “We do know that after a myocardial infarction, after a heart attack, that a lower ejection fraction does connote increased risk over the subsequent years,” Hadley Wilson, a cardiologist with the Sanger Heart and Vascular Institute, said to the Wall Street Journal last month.

In February, then-candidate Mike Bloomberg, who in 2000 had coronary stent placement surgery for a blocked artery, disclosed that his left ventricular ejection fraction was between 60 and 65 percent, a good reading. And he called on Sanders to reveal his measurement. (In December, Biden, who in 1988 had a cerebral aneurysm, released not his full medical records but a three-page report on his health that concluded he was “vigorous” and “fit” to serve as president.)

Without releasing the left ventricular ejection fraction, Sanders is certainly not engaging in full disclosure. A number of media outlets have pointed that out. And days ago I asked the Sanders campaign why Sanders was not sharing this indicator. “Wouldn’t ‘full disclosure’ include the release of this information?” I queried in an email.

Mike Casca, the communications director for the campaign, emailed a short reply, “The letters we released are very thorough.” But they aren’t. And I tried again: “[The letters] don’t include this measurement that coronary experts say is necessary to fully evaluate his heart after the heart attack. It would seem that his pledge of ‘full disclosure’ would cover this. Why would he not release it?”

Casca did not respond.

This is not to pick on Sanders, but as Democrats chose their 2020 nominee, age and health are significant factors. Biden is 77, Sanders a year older, and Donald Trump is 73. It’s a pack of septuagenarians. And they’re all publicly campaigning—and until yesterday had been holding rallies and shaking hands—in the middle of an epidemic that is particularly risky for men who are in the 70s and older. (On Tuesday, the Biden and Sanders campaigns canceled major rallies they had scheduled; the Trump campaign, defying the recommendations of public health experts, announced he would hold a large event in Milwaukee on March 19.)

During the 2008 campaign, Sen. John McCain’s health was an important issue. He was 71-years-old and then in the running to become the oldest person to assume the presidency, and he had faced several medical challenges, including skin cancer, since his days as a POW in Vietnam. He allowed reporters to review 1,173 pages of his medical records and to interview his doctors. No candidate has since met that standard.

When Trump was a candidate in 2015 he released a letter from a gastroenterologist declaring he “would be the healthiest individual ever elected to the presidency.” (This doctor later said he had written this letter in five minutes.) And Trump has recently not been forthright about his personal health matters. In November, he made an unscheduled trip to Walter Reed National Military Medical Center. Two days later, his doctor asserted this was for an “interim checkup,” and the White House described the visit as “phase one” of his annual physical. His previous annual physical, though, had been in February 2019—only nine months earlier. Medical experts noted that it was odd to have a “phase one” months before an annual check-up. And a few days ago, Trump said he would be completing his annual physical within the following 90 days. It makes little sense for a physical to include a “phase one” in November and then another round perhaps six months later. These actions and statements have prompted questions about Trump’s health and medical care.

Trump has dramatically lowered the bar for candidate transparency. (Still no tax returns!) But Sanders is doing the same when it comes to medical records. He made a clear promise. The condition of his heart is a legitimate subject for as long as Sanders remains a contender in the Democratic primary contest. Mortality rates can be high for older patients who have experienced heart attacks. And should anything happen to a presidential nominee before an election, it is unclear whether a party could get a replacement on every state ballot. So the health of a potential nominee—and that would include Biden, too—is a big deal. As Biden has moved closer to bagging the nomination, his opponents on the right and left have tried to raise questions about his cognitive abilities, often in a manner that seems designed as a smear. And, of course, Trump’s conduct has prompted concerns about his mental health and psychological well-being. These particular issues seem hard to address within the fury of a political debate. But in the instance of Sanders’ heart, there is an easy way to settle the matter. So why won’t he?