Charlie Riedel / AP

Updated on March 10 at 4:58 p.m. ET.

The first thing to go was the rope line.

Until this weekend, former Vice President Joe Biden would end his scripted rallies with a far more intimate tradition of campaign politics—by greeting his supporters personally, and physically. He’d press the flesh, high-fiving, shaking hands, leaning in close for photos with dozens, if not hundreds, of people crowded near the stage.

That ended on Saturday, when the campaign of the Democratic front-runner began taking its first, limited steps to prevent its 77-year-old candidate from contracting the coronavirus, which causes the disease known as COVID-19. Biden wasn’t exactly whisked away after speaking to a large crowd in St. Louis, but he greeted only those people who stood between him and his exit.

By last night in Detroit, an event staffer was greeting attendees lined up at the entrance to Biden’s rally in a high-school gymnasium with a squirt of hand sanitizer.

And this afternoon, Biden and his Democratic rival, Senator Bernie Sanders of Vermont, announced within a span of minutes that they were canceling their planned rallies in Cleveland tonight ahead of the Ohio primary next week. The campaigns said the cancellations were made out of concern “for health and safety” and after consultation with local officials. The separate decisions came after Ohio’s governor, Mike DeWine, a Republican, said that public-health experts had recommended banning spectators from sporting events and concerts.

The cancellations by Biden and Sanders mean that neither candidate is likely to address supporters in person on the night of key primaries in Michigan, Missouri, Mississippi, North Dakota, and Washington State.

This is the reality of campaigning during an epidemic, when the rapidly spreading coronavirus presents a danger not only to large crowds gathered at political rallies, but to the elderly candidates themselves. The Centers for Disease Control and Prevention is advising older adults to “avoid crowds as much as possible,” because research has found that death rates are significantly higher for people in their 60s, 70s, and 80s. The three major remaining contenders for the presidency—Biden, 77; Sanders, 78; and President Donald Trump, 73—are all in the high-risk category.

Sanders may be at even higher risk for a severe illness if he contracted the virus; he suffered a heart attack last year, and the CDC says people with chronic illnesses like heart disease are particularly vulnerable.

Navigating the crisis is tricky for both Democrats. The nomination fight is in its most intense phase, with major state primaries occurring tonight in Michigan and three other states, and in Ohio, Florida, and Illinois next week. Neither Biden nor Sanders can afford to scale back his campaign with so many delegates still at stake, and neither septuagenarian is eager to draw more attention to his advanced age and personal vulnerability to the coronavirus.

Trump, meanwhile, has scoffed at suggestions that he cancel the enormous rallies he relishes, or that he take extra precautions to avoid contracting the virus himself. The president has come into contact with at least two Republican congressmen who are self-quarantining after interacting with an attendee of the Conservative Political Action Conference who tested positive for the coronavirus. One of them, Representative Matt Gaetz of Florida, rode on Air Force One with Trump after his interaction with the infected person. “He was not hyper-cautious about being in the same space that I was in,” Gaetz said of the president, according to The Washington Post. “I refused to go into his office; I stood outside the door. I told him he could talk from that distance.”

Biden and Sanders have each criticized Trump for bungling and then downplaying the outbreak, yet until today, they have continued to hold rallies even as conferences, university classes, and other large gatherings are being canceled around the country.

“We do not hold a rally without first conferring with local public-health officials,” Sanders told reporters near the end of a roundtable he moderated on the coronavirus yesterday in Detroit. “But your question obviously goes to more than a political rally that I may have. It goes to basketball games; it goes to theater events all across this country. That is an issue that every organization, every sports team, is going to have to look at.

“It is an issue that we think about a whole lot,” he added.

Sanders had just spent an hour listening to a group of public-health experts warn about the seriousness of the outbreak, the risks of widespread transmission, and the Trump administration’s lack of preparedness. Yet when the question turned to his own health and safety—What precautions are you taking, given your age and recent heart attack? a reporter asked—the senator bristled.

“Well, I’m surrounded by medical personnel,” Sanders replied. “Thank you for asking. I am running for president of the United States, and that requires a whole lot of work.”

Alison Galvani, an epidemiologist who was seated next to Sanders, interjected that he was not shaking hands. She demonstrated by offering him her elbow. Sanders lifted his for a quick bump. “There we go,” he said. “All right.”

In addition to curtailing rope lines, Biden’s campaign was seeking guidance from the CDC on other steps, the former vice president told MSNBC’s Lawrence O’Donnell last night. He acknowledged the possibility of stopping indoor rallies altogether. “That’s all in motion right now,” Biden said.

Neither campaign was willing to discuss in detail what steps, if any, it had taken to protect its own employees, including those whose health might be compromised or on-the-ground organizers whose jobs require them to interact with voters.

Yet as the virus spreads, the rallies and face-to-face interactions that give life to their campaigns will seem riskier. After scrapping tonight’s rally, the Sanders campaign said future events would be evaluated “on a case by case basis.” If they resume, questions remain: Should Biden and Sanders discourage older Americans from attending their events, for example? Should they themselves cut off all physical contact with their supporters?

“The people of the United States,” Sanders said in Detroit yesterday, “want to know that we have an administration in this country whose decisions and comments are based on science, not based on tweets that have no scientific basis, not based on politics.”

For Sanders and his main rival, living up to that ideal could soon lead to some very uncomfortable decisions. Should the Democratic candidates merely follow the guidance and model of a president whose decisions they’ve denounced? Or should they lead by example?

“We ought to worry about everybody, but particularly about seniors,” Representative Donna Shalala of Florida, the former two-term secretary of health and human services under President Bill Clinton, told me when I asked her whether she was worried about Biden and Sanders. “I would like to see them do the same thing that we’re telling everybody else about large gatherings, about public-health measures,” she said. “They should not do anything that everybody else is not doing.”

In canceling their events today, the two Democratic hopefuls decided on the more conservative course.

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