“The C.D.C. issued the mandate in February 2021, almost two weeks after the president called for a mandate, 11 months after the president had declared Covid-19 a national emergency, and almost 13 months since the secretary of health and human services had declared a public health emergency,” she noted. “This history suggests that the C.D.C. itself did not find the passage of time particularly serious.”

In stressing that 11 months had passed between when the president declared a national emergency and when the agency imposed the mandate, Judge Mizelle did not address the fact that there had been a change of administration in that time.

As of Sunday, there was an average of more than 37,000 new cases a day, an increase of 39 percent from two weeks ago, according to a New York Times database.

Though the figure remains far lower than the peak of the winter surge driven by an Omicron variant, experts believe that new cases are increasingly undercounted with the rise of at-home testing. Also, many people who are vaccinated and have received booster shots have not experienced serious illness from contracting the Omicron variant.

Pulling back on the travel mask requirement at this moment is “very, very concerning,” Saskia Popescu, an infectious disease epidemiologist and assistant professor at George Mason University, said.

“We’re definitely starting to see a trend up in cases,” she said. “My concern is that we may see what happened in the U.K., where they drastically pulled back restrictions and saw a significant surge, and this will contribute to rising numbers.”

Charlie Savage reported from Washington, and Heather Murphy from New York. Reporting was contributed by Madeleine Ngo and Noah Weiland from Washington, and Niraj Chokshi, Adeel Hassan, Ana Ley and Roni Caryn Rabin from New York.