“There are so much toxic policies around Covid that they limit reasonable action,” he said. “Of course it makes sense in different settings to ask for proof of vaccination, but that has become a political lightning rod.”

Dr. Frieden and other experts said they fear that if the Delta variant continues to circulate, it will mutate in such a way that even the vaccinated will remain vulnerable. That already seems to be happening elsewhere in the world; even countries like South Korea and Israel, where the virus appeared to be in check, have new disease clusters.

“Compared to many other countries, we are in a much safer situation,” said Dr. Jennifer Nuzzo, an epidemiologist at Johns Hopkins University. But she added, “I really worry that while America is enjoying its freedoms, we are forgetting the rest of the world and that might come back to bite us.”

When Mr Biden announced his July 4th vaccination target in early May, he said the meeting would show that the United States had taken “a serious step towards a return to normal.” That seems to be the case with many. The president then said that Americans could gather in backyards for small Independence Day barbecues; Its gathering of 1,000 guests is intended to show the country, among other things, that its government has exceeded expectations, even if vaccinations have stalled.

While Mr Biden has repeatedly spoken of “independence from the virus,” Dr. Arthur L. Caplan, director of the Department of Medical Ethics at NYU Langone Medical Center, advised that the president should be careful with the language he uses.

“Before I had my fireworks and piña coladas on the White House porch, I said, ‘I have to make it clear as President that we have great challenges left unsolved,'” said Dr. Caplan. “I would say, ‘We’re good at halftime.'”

Dr. Anthony S. Fauci, the president’s top medical advisor for the pandemic, said the government’s message was not contradicting itself.