But Republican strategists and pollsters say Democrats should not be so quick to brush off the criticism, even if many Covid-related deaths this year were among those who ignored Mr. Biden’s entreaties to get vaccinated.

“McCarthy’s first hit on Biden is a competence hit — that he sold himself to voters as the guy who can make a difference in the fight against Covid, yet more Americans are dying,” said Neil Newhouse, a Republican pollster who has surveyed voters on the issue. “The bottom line is that Republicans have always been more focused on the economic impact of the pandemic, and now we’re seeing independents and swing voters expressing concern about those impacts as well: supply chain, inflation, jobs, stores not being open or having what they need.”

He added, “There is a sense that Biden’s presidency is falling short on its promises.”

The Thanksgiving wave is the latest surprise in a pandemic that is nearing its two-year mark. The nation’s 14-day average of new infections is up 25 percent, to over 94,000 new cases a day, with the upper Midwest again the hottest of hot spots. At the same time, the efficacy of the coronavirus vaccines is holding, according to the latest data from the Centers for Disease Control and Prevention. Unvaccinated people are 5.8 times as likely to test positive than fully vaccinated people, and 14 times as likely to die if infected.

The partisan gap in infection and vaccination rates is only slightly narrowing. The most Republican counties have 2.78 times as many new cases than the most Democratic counties, down from three times as many a month ago, according to the Democratic health care analyst Charles Gaba, using data from Johns Hopkins University. The death rate in those Republican counties is nearly six times as high as the death rate in the Democratic counties.

It is unclear whether the continuing pandemic or the vaccine mandates devised to beat it are causing the president’s approval ratings to slide. Mr. Newhouse’s firm, Public Opinion Strategies, found Mr. Biden’s overall approval rating for his handling of the pandemic to be a relatively fine 51 percent in October, down from 69 percent in April but only from 53 percent in August.

But in the suburbs, where the 2020 presidential race was won, the president’s approval rating on the pandemic has slipped since August from 51 percent to 45 percent. And among white men, the slide is more pronounced, from 58 percent in April to 43 percent in August and 32 percent in October.

Republican lawmakers are continuing to try to block vaccine mandates at the local, state and federal levels. In September, a proposal by Senator Roger Marshall of Kansas, an obstetrician, to block the use of federal funds to carry out the president’s vaccine mandate for businesses with at least 100 employees failed by one vote, after all 50 Republicans in the Senate backed it.