Sen. Rand Paul and Dr. Anthony Fauci clashed again during a Senate hearing, with the Kentucky Republican and the president’s chief medical adviser both accusing the other of lying when it came to the thorny subject of gain-of-function research at the Wuhan Institute of Virology.

Fauci, head of the National Institute of Allergy and Infectious Diseases, has been adamant National Institutes of Health grants did not fund gain-of-function research at the Wuhan lab but has also admitted he doesn’t actually know what the secretive Chinese lab has been up to.