‘Assume that you were exposed’: Officials warn of the fallout from Thanksgiving travel.

“Some of our numbers may be skewed by that,” he said.

The U.S. map shows a country where almost every region is a hot spot. States that were once spared, like Montana and Wyoming, have reported record deaths and infections, while states that were pummeled in the first wave are straining anew.

On Sunday, California became the first state to report more than 100,000 cases in a week, according to a New York Times database.

And in New Jersey, hospitalizations have increased 60 percent in the last two weeks and deaths have increased by 78 percent. Over three days in November, the positivity rate in Newark, the largest city in the state, was 19 percent.

“We begged people to have a somber, respectful, small Thanksgiving,” Gov. Philip D. Murphy said on Fox News Sunday. “And I want to give a shout out to New Jerseyans because I think overwhelmingly that’s what happened, but there’s a lot of fatigue out there.”

Mr. Murphy called the next few months “the fight of our lives,” while also citing the progress of vaccines and noting that there was “light at the end of the tunnel.”

And there was something to celebrate on Sunday in New York City, at least for some parents, when Mr. de Blasio announced that he would reopen the city’s public elementary schools, abruptly shifting policy after an outcry from critics who questioned why gyms and bars remained open while schools were shut.