“Everybody just assumes no one is going,” said Representative Darin LaHood of Illinois, an honorary state co-chairman for the Trump campaign.

Mr. LaHood was one of eight House members — from Illinois, New York, Arizona, Indiana and Michigan — who told The New York Times they did not plan to attend, joining party veterans like Senators Charles E. Grassley, Lamar Alexander and Susan Collins who have already said they will skip the event.

President Trump, in the meantime, may not get the restriction-free celebration he yearns for after all. The city of Jacksonville is requiring facial coverings in any public space where social distancing is not possible. And in a news release last week, the host committee said every attendee within the convention perimeter “will be tested and temperature checked each day,” without providing further details.

Still, even as growing numbers of elected leaders express wariness about attending, a strong contingent of Republican National Committee members — many of whom have their political fortunes tied to Mr. Trump — say they still plan to go. In interviews, more than a dozen of them said they were committed, even “proud,” to celebrate the renomination of Mr. Trump.