In a speech to Kentucky voters not that long ago, Hillary Clinton said that, if elected, she would put her husband “in charge of revitalizing the economy because, you know, he knows how to do it.”

She didn’t elaborate on what exactly she’d have Bill Clinton do — especially since sitting presidents already have a treasury secretary (a cabinet position) and the National Economic Council as part of their large team of official advisers.

Hillary struggles with blood clots and takes blood thinners to prevent dangerous coagulation. Bill has undergone open-heart surgery twice.

It’s hard to see Bill Clinton interested in any of the traditional duties of the “first spouse” — and many voters are afraid that a vote for Hillary would actually mean four more years of Bill Clinton in the Oval Office.

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But as Hillary’s health problems become increasingly alarming, the eyes of Americans turn again toward Bill Clinton. The role of presidential spouse often means stepping in for the president when needed, whether due to health problems or busy schedules. When President Ronald Reagan was shot in 1981 and underwent surgery, Vice President George H.W. Bush stepped up as needed. But Nancy Reagan also stepped up — she took a prominent role in security and scheduling, and in some ways became President Reagan’s closest adviser.

Nancy Reagan was 60 years old when her husband took office. Bill Clinton, by contrast, is a full decade older than that. And there’s strong evidence he wouldn’t be healthy enough to fill in for Hillary if the need ever arose.

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People closest to Bill Clinton have noted a marked change in his health and appearance in recent years. Age has not agreed with him. Jason Zingerle, a political correspondent from GQ, describes his speeches during this campaign season: “Up close, his appearance was a shock. The imposing frame had shrunk, so that his blue blazer slipped from his shoulders, as if from a dry cleaner’s hanger, and the collar of his shirt was like a loose shoelace around his neck. His hair, which long ago had gone white, was now as thin and downy as a gosling’s feathers, and his eyes, no longer cornflower blue but now a dull gray, were anchored by bags so dark it looked like he’d been in a fight. He is not a young man anymore — he’ll turn 70 in August — but on this afternoon, he looked ancient.”

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Bill Clinton’s health has deteriorated since his quadruple-bypass surgery in 2004. After he had significant chest pains, doctors took large blood vessels from elsewhere in his body and rerouted the blood to his heart to bypass blocked arteries. He had follow-up surgery six months later to clear the scar tissue from his lungs. In order to prevent future heart problems, Clinton has adopted a vegan diet — and subsequently dropped a significant amount of weight. To many of his former fans, he looks like a shadow of himself.

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Related: Hillary’s ‘Fit to Serve’ Report: Unbelievable

It seems poor heart health haunts both the Clintons these days. Hillary struggles with blood clots and takes blood thinners to prevent dangerous coagulation. Bill has now undergone open-heart surgery twice. He developed blockages in two of the arterial bypasses again in 2010, and doctors placed two stents to hold open the passageways to his heart.

His doctors have been clear: There’s nothing Bill Clinton can do to stop these blockages. Despite his adoption of a vegan lifestyle, this condition isn’t going away. They’re not an issue of diet, lifestyle, or cholesterol. Even patients who do everything right will continue to have this problem because heart disease is progressive and cannot be cured by surgery. “This is a chronic condition,” said Dr. Allan Schwartz, Clinton’s cardiologist, in a media release. “We don’t have a cure.”

His doctors have been clear: There’s nothing Bill Clinton can do to stop these blockages.

Heart problems aren’t the only health concern to plague Bill Clinton. His hands now continually shake during his speeches, and he can only control them by shoving them into his pockets or gripping the podium. In an interview in 2013, he admitted: “I have a condition that sometimes you get with aging. You may have noticed it; my hand has a little tremor when I’m tired and a lot of people do when they’re older.”

His shaking hands caused a stir on Twitter during the Democratic National Convention, even among his fans.

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If Hillary’s health continues to deteriorate, it’s important to figure out who would be running the White House during her convalescence if she were to win the election in November. In the case of serious illness, which seems more and more likely, what would Tim Kaine step up to do — and what might Bill Clinton take on from his vantage point? Both Donald Trump and his running mate Gov. Mike Pence have reaffirmed their good health and active lifestyles. It’s obvious the Clintons cannot say the same.