Dr. Peter Marks is the kind of health official both Democrats and Republicans used to admire. He served in the U.S. Food and Drug Administration (FDA) for 13 years, most of them as director of the Center for Biologics Evaluation and Research. There, Marks oversaw the critical process of reviewing and approving vaccines—like those against COVID-19—and biologic therapies, including gene- and cell-based treatments.

Marks earned trust and respect from academic and industry scientists as well for his emphasis on requesting the strongest evidence in evaluating new therapies, and for his willingness to support new technologies and approaches.

But he did not last long in the new Trump Administration. On March 28, Marks resigned after he says he was pressed by Department of Health and Human Services (HHS) officials to come in line with skepticism about the safety and effectiveness of vaccines or be fired. He says his team was also asked by HHS to turn over sensitive health information from the database the FDA maintains with the U.S. Centers for Disease Control and Prevention (CDC) to track adverse reactions to vaccines. Concerned about how the data would be used, Marks refused and resigned. (HHS did not immediately respond to a request for comment for this story.)

Now, he is warning of a fundamental change at HHS and the FDA—one he believes is already proving to be very dangerous. “What I saw at the agency was an increasing anti-vaccine tone," he told TIME On April 8. "I was hoping to work through it, but it was very clear to me that they just didn’t want to work through it.”