SALT LAKE CITY (AP) — One of the Republican Party’s most prominent rising stars is mocking new government recommendations calling for more widespread use of masks to blunt a coronavirus surge.

“Did you not get the CDC’s memo?” Florida Gov. Ron DeSantis joked Wednesday before an almost entirely unmasked audience of activists and lawmakers crammed into an indoor hotel ballroom in Salt Lake City. “I don’t see you guys complying.”

From Texas to South Dakota, Republican leaders responded with hostility and defiance to updated masking guidance from public health officials, who advise that even fully vaccinated people return to wearing masks indoors if they live in areas with high rates of virus transmission. The backlash reopened the culture war over pandemic restrictions just as efforts to persuade unvaccinated Americans to get shots appeared to be making headway.

Egged on by former President Donald Trump, the response reflects deep resistance among many GOP voters to restrictions aimed at containing a virus they feel poses minimal personal threat. The party is also tapping into growing frustration and confusion over ever-shifting rules and guidance.

But the resistance has real implications for a country desperate to emerge from the pandemic. Beyond vaccinations, there are few tools other than mask-wearing and social distancing to contain the spread of the delta variant, which studies have shown to be far more contagious than the original strain.

Many Republican leaders, however, are blocking preventative measures, potentially making it harder to tame virus outbreaks in conservative communities.

At least 18 Republican-led states have moved to prohibit vaccine passports or to ban public entities from requiring proof of vaccination. And some have prohibited schools from requiring any student or teacher to wear a mask or be vaccinated.

In its announcement, the CDC cited troubling new — thus far unpublished — research that found that fully vaccinated people can spread the delta variant just like the unvaccinated, putting those who haven’t received the shots or who have compromised immune systems at heightened risk. The CDC also recommended that all teachers, staff and students wear masks inside school buildings, regardless of vaccination status.

The backlash was swift.

“We won’t go back. We won’t mask our children,” declared Trump, who routinely cast doubt on the value of mask-wearing and rarely wore one in public while he was in office. “Why do Democrats distrust the science?”

Missouri Gov. Mike Parson called the new guidance “disappointing and concerning” and “inconsistent with the overwhelming evidence surrounding the efficacy of the vaccines and their proven results.”

He, like others, warned that the measure would undermine efforts to encourage vaccine holdouts to get their shots by casting further doubt on the efficacy of approved vaccines, which have been shown to dramatically decrease the risk of death or hospitalization, despite the occurrence of breakthrough cases.

Last week, White House officials reported that vaccination rates were on the rise in some states where COVID-19 cases were soaring, as more Republican leaders implored their constituents to lay lingering doubts aside and get the shots to protect themselves. That includes Alabama Gov. Kay Ivey, who has pleaded with unvaccinated residents, saying they are the ones “letting us down.”

“This self-inflicted setback encourages skepticism and vaccine hesitancy at a time when the goal is to prevent serious illnesses and deaths from COVID-19 through vaccination,” Parson tweeted. “This decision only promotes fear & further division among our citizens.”

The announcement “will unfortunately only diminish confidence in the vaccine and create more challenges for public health officials 一 people who have worked tirelessly to increase vaccination rates,” echoed Arizona Gov. Doug Ducey, who has banned mask and vaccine mandates in his state.

In his Wednesday speech, DeSantis took particular aim at the CDC’s call for kids to wear masks in the classroom.

“It’s not healthy for these students to be sitting there all day, 6-year-old kids in kindergarten covered in masks,” he said — though there is no evidence that wearing masks is harmful to children older than toddler age.

And in South Dakota, Gov. Kristi Noem called out the CDC for shifting its position on masking “AGAIN.” She said that those who are worried about the virus can get vaccinated, wear a mask or stay home, but that “Changing CDC guidelines don’t help ensure the public’s trust.”

On Capitol Hill, some Republicans were in revolt after the Capitol’s attending physician sent a memo informing members that masks would again have to be worn inside the House at all times.

The change set off a round robin of insults, with Democratic House Speaker Nancy Pelosi calling Republican House Minority Leader Kevin McCarthy “a moron” after McCarthy tweeted, “The threat of bringing masks back is not a decision based on science, but a decision conjured up by liberal government officials who want to continue to live in a perpetual pandemic state.”

The mandate also prompted an angry confrontation, as Rep. Maxine Waters, D-Calif., verbally assailed Rep. Burgess Owens, R-Utah, who exited the House chamber and walked past her without a face covering.

Conservatives also forced a vote to adjourn the chamber in protest to the mandate, which was defeated along mostly party lines.

“We have a crisis at our border, and we’re playing footsie with mask mandates in the people’s House,” railed Rep. Chip Roy, R-Texas, the motion’s sponsor. “The American people are fed up. They want to go back to life. They want to go back to business. They want to go back to school without their children being forced to wear masks.”

The nation is averaging nearly 62,000 new COVID-19 cases a day, and the vast majority of those hospitalized and dying haven’t been vaccinated. As of Sunday, 69% of American adults had received one vaccine dose, and 60% had been fully vaccinated, according to the CDC.

Last year, early on in the pandemic, public health officials told Americans that masks offered little protection against the virus (and could even increase the risk of infection). The guidance was driven by a lack of knowledge about how the novel virus spread and a desire to save limited mask supplies for medical workers. But the CDC soon changed course and advised Americans to wear masks indoors and outdoors if they were within 6 feet (1.8 meters) of one another.

Then in April of this year, as vaccination rates rose sharply, the agency eased its guidelines, saying fully vaccinated Americans no longer needed to wear masks outdoors unless they were in big crowds of strangers. In May, the guidance was eased further, saying fully vaccinated people could safely stop wearing masks outdoors in crowds and in most indoor settings.

Subsequent CDC guidance said fully vaccinated people no longer needed to wear masks at schools, either.

Karine Jean-Pierre, the White House principal deputy press secretary, on Wednesday defended the changes, saying the CDC “did exactly what it was supposed to do.”

“The CDC has to adapt to the virus,” she said, “and unfortunately because not enough Americans have stepped up to get vaccinated, they had to provide new guidance to help save lives.”

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Colvin reported from Washington. Associated Press writers Jonathan J. Cooper in Phoenix, Alan Fram in Washington, Summer Ballentine in Jefferson City, Mo., and Alexandra Jaffe aboard Air Force One contributed to this report.

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This story has been corrected to delete an erroneous reference to Alabama having prohibited schools from requiring masks. The state is allowing local school districts to make that decision.