The Trump administration’s latest nominee to lead the nation’ top public health agency drew frustrated reactions from some U.S. senators when they pressed her on whether she would protect the Centers for Disease Control and Prevention from political meddling.

Jennifer Shuford, an infectious disease physician who oversaw the country’s largest measles outbreak in 30 years, is among a slate of CDC nominations with no apparent ties to the anti-vaccine movement.

President Donald Trump has nominated Erica Schwartz, a former deputy surgeon general, to be the next director of the Centers for Disease Control and Prevention.