WASHINGTON — President Biden’s aggressive push to require millions of U.S. workers to get vaccinated against the coronavirus is running into a wall of resistance from Republican leaders threatening lawsuits and civil disobedience, plunging the country deeper into culture wars that have festered since the onset of the pandemic.

In South Carolina, Gov. Henry McMaster says he will fight “to the gates of hell to protect the liberty and livelihood of every South Carolinian.” South Dakota Gov. Kristi Noem, a potential 2024 presidential candidate, says she is preparing a lawsuit. And J.D. Vance, a conservative running for a U.S. Senate seat in Ohio, is calling on businesses to ignore mandates he describes as Washington’s “attempt to bully and coerce citizens.”

“Only mass civil disobedience will save us from Joe Biden’s naked authoritarianism,” Vance says.

Biden is hardly backing down. In a visit to a school Friday, he accused the governors of being “cavalier” with the health of young Americans, and when asked about foes who would file legal challenges, he retorted, “Have at it.”

U.S. studies released Friday show the COVID-19 vaccines remain highly effective against hospitalizations and death even with the highly contagious Delta variant. As Delta surged in early summer, those who were unvaccinated were 4 ½ times more likely than fully vaccinated people to get infected, over 10 times more likely to be hospitalized and 11 times more likely to die, according to the Centers for Disease Control and Prevention.

“Vaccination works,” Dr. Rochelle Walensky, the CDC’s director, said at a White House briefing Friday. “The bottom line is this: We have the scientific tools we need to turn the corner on this pandemic.”

The Republican opposition follows Biden’s announcement Thursday of a major plan to tame the coronavirus as the Delta variant drives 1,500 deaths and 150,000 cases a day. Biden is mandating that all employers with more than 100 workers require their employees to be vaccinated or test for the virus weekly, affecting about 80 million Americans. An additional 17 million workers at health facilities that receive federal Medicare or Medicaid also will have to be vaccinated, as will all employees of the executive branch and contractors who do business with the federal government.

The move brought Republican outrage from state capitals, Congress and the campaign trail, including from many who have supported vaccinations and have urged their constituents to take the shots.

“The vaccine itself is life-saving, but this unconstitutional move is terrifying,” tweeted Mississippi Gov. Tate Reeves.

Texas Rep. Dan Crenshaw, who has promoted the vaccines’ safety, tweeted, “The right path is built upon explaining, educating and building trust, including explaining the risks/benefits/pros/cons in an honest way so a person can make their own decision.”

More than 208 million Americans have received at least one vaccine dose, but some 80 million remain unvaccinated, driving infections. There are now about 300% more new daily infections, about 2 ½ times the hospitalizations and nearly twice the number of deaths as at the same time last year.

The pandemic is worsening in many of the states where governors are most loudly protesting the president’s actions. South Carolina, for example, is averaging more than 5,000 new cases a day and has the nation’s second-highest infection rate. A hospital system there started canceling elective surgeries last week to free staff to help with a crush of COVID-19 patients.

In a section of Idaho, overwhelmed hospitals have implemented new crisis standards to ration care for patients. And in Georgia, hospitals have been turning away ambulances bringing emergency or ICU patients.

“I am so disappointed that particularly some Republican governors have been so cavalier with the health of these kids, so cavalier with the health of their communities,” Biden said during his school visit. “This isn’t a game.”

But Republicans and some union officials say the president is overreaching his constitutional authority. They take issue, in particular, with the idea that millions could lose their jobs if they refuse to take the shots.

“That’s a ridiculous choice,” said Mississippi’s Reeves.

Biden, however, says he’s doing what needs to be done to fight resistance that has continued despite months of encouragement and incentives. In his White House speech announcing the new measures, he was visibly frustrated, criticizing the remaining holdouts and accusing some elected officials of “actively working to undermine the fight against COVID-19.”

“Instead of encouraging people to get vaccinated and mask up, they’re ordering mobile morgues for the unvaccinated dying from COVID in their communities,” he said.

Court fights are sure to follow in a number of states.

Vaccine mandates are supported by a majority of Americans. An August poll from the Associated Press-NORC Center for Public Affairs Research found majorities support requiring vaccinations for healthcare workers, teachers at K-12 schools and public-facing workers such as those who work in restaurants and stores. Overall, 55% back vaccine mandates for government workers. And about half of working adults favor vaccine mandates at their own workplaces.

But the numbers are deeply polarized, with Democrats far more likely to support mandates than Republicans, who have also been less supportive when it comes to getting shots.

Although demand for vaccinations has risen over the summer, a persistent number of Americans have said they have no intention of ever receiving the shots.

GOP pollster Frank Luntz, who has held focus groups and worked with the Biden administration to try to combat vaccine hesitance, says that, without further measures, Biden is likely to see vaccinations top out at about 75% of the population.

“The only way to exceed that, which he needs to for herd immunity, is to mandate it,” Luntz said. “It will make a lot of people angry and even more resistant, but those who are simply hesitant will act now. He’s done the best he can under the circumstances.”

Colvin writes for the Associated Press.