Michelle Mello, a medicine and law professor at Stanford University in California, said there are two parallel groups of mandate opponents: people who are invoking personal or religious freedom to skip vaccinations, and right-wing politicians speaking to voters primed by 18 months of politicization about the virus in general.

Mello, 48, said it’s unclear whether politicians truly oppose vaccine mandates or if they’re simply riding a wave of populism, even though polls show the American public generally supports COVID-19 vaccine mandates. For decades, almost every schoolkid in the country has faced mandatory vaccinations for everything from polio to tetanus and diphtheria.

“Maybe a clue is that none of them ever had a problem with any other vaccine mandate ever,” Mello said.

Mello said she’s watching to see how the Biden administration and the Supreme Court handle the growing number of people seeking religious exemptions despite never previously objecting to vaccinations. Several Republican attorneys general plan to sue the Biden administration on religious- and personal-freedom grounds once the mandates are formally introduced, and 21 of them on Wednesday sent Biden a letter raising objections.

The United States has a long history of permitting people with deeply held religious beliefs to skip vaccines, but the U.S. Equal Employment Opportunity Commission this week specified that “objections to COVID-19 vaccination that are based on social, political, or personal preferences” don’t qualify for an exemption.

Mello said it’s language like that, and questions about whether Catholics can claim an exemption even though the pope recommends vaccinations, that will put the Biden mandates before the Supreme Court.

“I think the most likely outcome is we will continue to see people die in states with legislatures and governors behaving irrationally about what works and doesn’t work in controlling COVID,” she said.