Democratic officials are instructing House and Senate members and party delegates to skip attending their national convention this summer, a sign of the ever-shrinking aspirations for their big campaign event in the face of surging coronavirus cases in the United States.

“We have been working closely with state and local public health officials, as well epidemiologists, and have come to the hard decision that members of Congress should not plan to travel to Milwaukee,” Chasseny Lewis, a senior adviser to the convention committee, wrote in an email to congressional aides. “No delegates will travel to Milwaukee and Caucus and Council meetings will take place virtually.”

The directive ensures that little will happen at the physical convention site beyond keynote speeches from former Vice President Joseph R. Biden Jr., his vice-presidential nominee and a handful of other top party leaders. The remainder of the event — state delegation meetings, parties and schmoozing, voting on the party platform and Mr. Biden’s nomination — will happen virtually or not at all.