and is once again at "another pivotal point in this pandemic" as the highly infectious Delta variant rips through communities with low rates of vaccination.

The warning from the director, Dr. Rochelle Walensky, during a briefing by members of the White House Covid-19 response team, was a marked shift from just weeks ago, when President Biden threw a big Fourth of July party on the South Lawn of the White House to declare independence from the virus.

It reflects a growing concern among administration officials that the gains they appeared to have made are being erased — and that the current surge in cases will overwhelm health systems in parts of the country where vaccination rates are low and hospitalizations are high.