The Biden and Sanders campaigns have addressed the coronavirus more often and directly than Mr. Trump in their emails to supporters, and both continued to solicit contributions as the crisis has deepened, though Mr. Sanders stopped on Wednesday as he reassessed his candidacy.

So far Mr. Trump’s campaign stands alone in trying to create his own virtual reality, mostly ignoring the virus (with the exception of one email and text message a week ago linking to C.D.C. guidance), belittling Democrats and bashing the media even as the outbreak has upended almost every facet of American life.

Some public health officials said that, given the partisan divide on how seriously Americans are taking the virus threat, Mr. Trump could have made an impact with more and earlier messages, including to his extensive email list, encouraging people to stay home and practice social distancing.

In an NBC/Wall Street Journal poll last week, more than two-thirds of Democrats worried an immediate family member would catch the coronavirus, compared to only 40 percent of Republicans.

“If he — in his political vehicle — if he was telling them this was really serious, you need to take this seriously, you need to understand what social distancing is, you need to stay home, you need to wash your hands, it would be a real benefit,” said Diana Dooley, a former secretary of the California health and human services agency. “He had this opportunity to do that through his political machinery.”

The frequency of Trump campaign emails has slowed in recent days. But the tenor has remained the same: The campaign has hawked a signed “Keep America Great” hat, sold “Trump Luck of the Irish Whiskey Glasses” for St. Patrick’s Day and offered an exclusive “gold card” membership for donors of $35 and up. One email on Wednesday bragged about “record-low” unemployment figures, as administration officials raced to stave off a massive hike in joblessness. On Thursday, Mr. Trump’s campaign asked the “patriots” on his list to hit a “MASSIVE” $2 million fund-raising goal.

The gap between the Trump campaign’s boosterism and the unsettling reality of a nation under siege from a deadly contagion can be jarring, even if it goes unseen by most Americans — unless they are among the millions who have opted to receive Mr. Trump’s online campaign missives.