The past four presidents, for their many differences, all distinguished themselves with an ability to excel in a room, either through soaring speechmaking (Barack Obama), rampaging rally (Mr. Trump) or a talent for insta-connections with voters in smaller, unrehearsed settings (Bill Clinton and George W. Bush).

Certainly all three major 2020 candidates are being stripped of some signal political strengths during the hiatus. Mr. Trump’s events are something akin to oxygen for him, rousing his base and supplying the live-action feedback and adulation he craves.

Mr. Biden’s best moments often come on the voter rope-line after he leaves the lectern, showcasing his empathy and charm — and his eagerness to shake hands, shoulders, anything in range — more effectively than his public remarks tend to. (Other flourishes, like his recent profanity-specked exchange with a man in Michigan, who suggested Mr. Biden wanted to confiscate guns, can also flow from these interactions, for better or worse.)

The Sanders campaign has been perhaps the nimblest and most experienced with virtual gatherings and social media-driven events long before the outbreak, powered in part by the youth and tech savvy of the senator’s core supporters.