It's not just vaccine mandates, but also the idea of vaccine passports that have caused controversy in the US. Despite already being used in other nations, prominent Republicans like Donald Trump Jr have opposed passports as well, making it hard to combat the coronavirus in the US. From the public, the fear of vaccines appears to have spread to the US military as well, if you believe Massie.
U.S. Air Force Sgt. Gerald Allen receives a dose of the Moderna COVID-19 vaccine at Osan Air Base on December 29, 2020, in Pyeongtaek, South Korea. (United States Forces Korea via Getty Images)