The union representing thousands of workers at the U.S. Centers for Disease Control and Prevention is calling on the Trump administration to condemn vaccine disinformation.

"Kennedy is directly responsible for the villainization of CDC's workforce through his continuous lies about science and vaccine safety, which have fueled a climate of hostility and mistrust," one ex-employee wrote, according to the Associated Press news agency.

As he grappled with those issues, sources said, White had become increasingly fixated on the COVID-19 vaccine as a source of his grievances. Several Kennesaw residents who knew the 30-year-old suspected shooter told ABC News they had heard White express similar angry and conspiracy-minded sentiments.