DEARBORN HEIGHTS, Mich. — Outside a polling place, Senator Bernie Sanders of Vermont did a few fist bumps. He clasped some shoulders. There were high fives and, yes, he shook a couple hands.
At an auto plant that is under construction, former Vice President Joseph R. Biden Jr. shook hands and posed for pictures as workers in hard hats and fluorescent vests crowded around him.
Fears about the coronavirus, which is often spread through person-to-person interaction, led Mr. Sanders’s campaign to announce on Tuesday afternoon that it was canceling a rally that night in Cleveland. Soon after, Mr. Biden’s campaign canceled its own Tuesday night rally in Cleveland.
But while they have now taken large-scale precautionary measures, Mr. Sanders and Mr. Biden have been greeting voters in recent days pretty much how they always have.
As public health officials warn Americans not to touch their faces and avoid handshakes with strangers, the two leading Democratic presidential candidates, both septuagenarians wary of changing their decades-old campaign methods, have endeavored to touch as many people as they can, both literally and figuratively.
The first public appearance for Mr. Sanders on Tuesday, when Michigan has the most delegates available among six states holding nominating contests, came at an early afternoon chat with reporters and a few dozen supporters outside a community center in Dearborn Heights.
Navigating a crush of cheering fans gathered on the sidewalk, Mr. Sanders executed a technique familiar to swimmers and football pass rushers, tapping people on the shoulders and forearms to get to his appointed spot to address the awaiting cameras.
Asked if he was still shaking hands given the coronavirus warnings, Mr. Sanders said he was trying to.
“We do — not as much, I don’t think, as we used to,” he said.
Mr. Sanders said his campaign was taking the health threats seriously and would not host rallies, which tend to draw thousands of supporters packed into tight spaces, if local officials weren’t on board. It could become difficult for Mr. Sanders to demonstrate the energy and enthusiasm he often highlights if he is forced to cancel more future rallies.
“What we are doing wherever we go, whenever we do rallies, we consult with public health officials, because the last thing we want to do is put anybody in danger,” he said.
While Mr. Sanders has plenty of in-person contact on the trail, he has never been a touchy-feely politician. Coronavirus restrictions have the potential to be particularly disruptive for Mr. Biden, a tactile campaigner who thrives in one-on-one interactions with voters.
After rallies in recent days, he has not lingered on the rope line, though it was not clear to what extent that decision was a response to concerns over the coronavirus. Mr. Biden has been drawing much bigger crowds at recent rallies than he did in Iowa and New Hampshire, so staying behind to meet voters one at a time may be less practical.
When Mr. Biden sat down for lunch at a Southern buffet-style restaurant in Jackson, Miss., on Sunday, he rubbed sanitizer on his hands. When he visited a high school in Detroit for a Monday night rally, which his campaign said drew 2,000 people, attendees were given hand sanitizer as they entered the event. And on Tuesday, when he visited a new Fiat Chrysler Automobiles assembly plant in Detroit, he continued his usual practice of greeting strangers in a hands-on fashion.
The Biden campaign said in a statement on Sunday that Mr. Biden and his team would “lead by example in following expert advice and complying with reasonable risk mitigations.”
Beyond the Cleveland rally on Tuesday night that was canceled, he has additional public events scheduled in Tampa, Fla., Chicago and Miami in the coming week.
Mr. Biden told NBC News that he was following the recommendations of the Centers for Disease Control and Prevention.
“I’m looking to the C.D.C. for advice,” he said. “If you notice in here, we did a fist bump, we didn’t shake hands. Well, I think that we’re going to follow the recommendations of the experts, and if they conclude that there shouldn’t be big indoor rallies, then we’ll stop big indoor rallies. We’re going to do whatever they say.”
After Mr. Sanders concluded a rally in St. Louis on Sunday, he engaged in his typical physical contact with top surrogates and supporters. He and the half-dozen people who spoke before him onstage all put their arms around one another for photographs, and Mr. Sanders then shook hands with several people who had been standing behind him during his 44-minute speech.
Later Monday, Mr. Sanders added to his schedule a hastily arranged news conference at the Westin hotel near a Detroit airport to discuss how he would respond to the coronavirus if he were president.
Asked what precautions he was taking to keep himself healthy, Mr. Sanders gestured to the table where he sat with prominent surrogates, who included Dr. Abdul El-Sayed, the former Detroit public health director, and Deborah Burger, a nurse who is the president of the National Nurses United union, which backs his campaign.
“Well, I’m surrounded by medical personnel,” he said. “I’m running for president of the United States, and that requires a whole lot of work.”
Reid J. Epstein reported from Dearborn Heights, and Thomas Kaplan from Detroit.