Presidential challengers always prize three moments of dayslong publicity — with their vice-presidential selection, their conventions and in the fall debates. That sustained coverage is all the more important now that the virus is likely to keep Mr. Biden off the campaign trail for much of the spring and may substantially condense the general election period.

“There are things you can do online, but there is something about the communal spirit that is important and people feed off of,” said David Axelrod, a senior official in Barack Obama’s presidential campaigns. “From a television standpoint it’s hard to have the same impact if you’re cobbling together a series of remotes.”

Though an in-person convention would provide Mr. Biden a nationally televised boost, the later date carries potential downsides. In addition to potentially keeping Mr. Biden out of the spotlight for an extended period of time, it could complicate his timing on when to announce his vice-presidential choice. And it delays for a month his ability to access funds earmarked for the general election.

Concerns over the virus have already led to the cancellation of hundreds of state and local conventions from both parties. Moving the national convention back a month is an acknowledgment that the outlook for holding an in-person gathering in July — with some 4,500 delegates, and tens of thousands of others who convene on the convention city — was not feasible.

“We welcome the D.N.C.’s decision today to prioritize the health and safety of delegates and the greater Milwaukee community by postponing the Democratic National Convention until August,’’ said Bill Russo, a campaign spokesman, adding that the campaign would continue to work closely with state parties and the D.N.C. “on any changes to the delegate selection process and the format of the convention.”

But there is no guarantee that the crisis will be over by August, and travel could still be difficult or even dangerous for some. One of Mr. Biden’s strongest constituencies is older Americans, the population most vulnerable to the virus, and the lingering effects of the outbreak could still have an effect on which delegates are able to travel.

Dr. Irwin Redlener, a clinical professor at Columbia University’s Mailman School of Public Health, said he was deeply skeptical of a summer convention.