But either way, the Mar-a-Lago petri dish has become a kind of metaphor for the perils of group gatherings in the age of coronavirus, demonstrating how quickly and silently the virus can spread. No one is necessarily safe from encountering it, not senators or diplomats or even the most powerful person on the planet seemingly secure in a veritable fortress surrounded by Secret Service agents.

Some of last weekend’s guests worried it may be a sign of the times and the last party of its sort for a while at Mar-a-Lago. “I hope not,” Representative Matt Gaetz, Republican of Florida, wrote in a text message. “Humans interacting with one another are typically happier and more productive in my experience.”…

Despite the coronavirus, the president has not changed his practice of greeting guests, according to a member. Mr. Trump believes his willingness to shake hands and connect with supporters helped propel him into office and the club’s unwritten rule is that those who love him or trade on connections with him can come into contact with him.