ALTOONA, Iowa ― Vermont Sen. Bernie Sanders, a leading candidate for the 2020 Democratic presidential nomination, got a warm welcome at a gathering of the United Food and Commercial Workers union at a casino in this Des Moines suburb. The International President of the UFCW, Marc Perrone, praised him as a “liberal lion” who had changed the debate on health care and economic policy. At the end of Sanders’ speech, the roughly 400 union members stood and applauded. There was one problem, if you could call it that: Sanders wasn’t in Altoona. While Democratic candidates major (former Vice President Joe Biden) and minor (Colorado Sen. Michael Bennet) had flown to Iowa for the event, Sanders appeared from the living room of his family home in Burlington, Vermont, and delivered his speech via Skype. As new polling suggests Sanders’ heart attack may harm his chances to win the nomination, his campaign is working to project normalcy, even as Sanders remains at home under doctor’s orders. Sanders is set to make his first public appearance outside of Vermont since the health scare on Tuesday night at the fourth Democratic presidential debate in the suburbs of Columbus, Ohio ― an appearance his campaign hopes will quiet doubts about whether he can win the nomination. Sanders’ speech at the UFCW forum was his standard fare: He promised “Medicare for All,” a $15 minimum wage, doubling union membership in his first term, and floated the possibility of making the work week shorter. (Sanders’ friendly welcome from the UFCW crowd wasn’t a total surprise: The union represents his campaign staff.) “You’ve proven no matter what may come, you’ll never shrink from a righteous fight,” Perrone said before Sanders spoke. “You’ve had a cardiac event, and you still wanted to be here with us.” Sanders has made himself available to reporters multiple times in the past week and sat for an interview with ABC News on Sunday, hoping to continue to get his campaign’s message out, even if he’s unable to travel to the early states. In a new HuffPost/YouGov survey, 88% of registered voters say they’ve heard at least a little about Sanders having a heart attack. The news appears to have taken a toll on perceptions of his health ― just 19% of voters say they believe he is in good enough physical condition to serve effectively as president for four years. By comparison, 43% believe former Vice President Joe Biden is in adequate health, with 53% saying the same of President Donald Trump and 66% of Massachusetts Sen. Elizabeth Warren.

SOPA Images via Getty Images Vermont Sen. Bernie Sanders will attend Tuesday night’s presidential debate in Ohio. He’s been confined to Vermont in recent weeks following a heart attack.

Views of the candidates’ health are clearly, to some extent, motivated by politics: 85% of Republican and Republican-leaning voters consider Trump physically healthy enough to serve, while only a quarter of Democrats and Democratic-leaners say the same. But even those on Sanders’ side of the aisle are expressing concerns. Just 28% of Democrats and Democratic-leaning voters say they think Sanders is in physical condition to serve effectively, compared to the 59% who say the same of Biden and the 81% who say the same of Warren. More broadly, a 56% majority of voters say they believe Sanders’ age would make it difficult for him to serve effectively as president, with 44% saying the same of Biden, who was born the year after him. Only a third are similarly concerned about Trump’s age. Warren, perhaps helped by the fact that many voters believe her to be younger than she is, fared best on the metric, with just 16% saying her age would make it difficult for her to serve. It’s not yet clear whether or to what extent these concerns will eat into Sanders’ standing in the horse race, which has remained relatively stablein aggregate for months.

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HuffPost US

HuffPost US

Polling that focuses specifically on the candidates’ age may overstate the degree to which voters are making their decisions on that basis. The electorate may not be pining for a septuagenarian president ― just 3% of Democrats say they’d consider that ideal, per one survey ― but that hasn’t stopped them from advancing a trio of candidates in their 70s to front-runner status against an incumbent of similar age. There’s also potential room for specific worries about a candidate’s health to recede. In a 2016 Economist/YouGov poll taken after Hillary Clinton suffered a bout with pneumonia, only 45% of voters thought she was in physical condition to serve as president; within two weeks, however, that number had recovered to 52%, close to where she’d stood earlier in the campaign. (That same poll put confidence in Trump’s physical health in the mid-60s, significantly better than his current standing.) Voters say, 64% to 22%, that it’s fair for the media to question a candidate’s physical health. They’re more divided on how much information candidates should be expected to provide about their health. About half say candidates should publicly release all medical information that might affect their ability to serve, while 39% say the candidates should have the right to keep their records private. Democratic voters are more than twice as likely as GOP voters to say candidates should release all their medical information ― a reversal from 2016, when Republicans were the party more likely to favor such disclosure and to consider media scrutiny fair game.

Scott Olson via Getty Images Sanders spoke to the UFCW gathering via Skype.