A former Republican member of Congress on Sunday put his onetime colleagues on notice after The New York Times reported on details from a draft outline of former national security adviser John Bolton’s forthcoming book.

Bolton recalls President Donald Trump saying he wanted to withhold aid to Ukraine until the nation agreed to investigate former Vice President Joe Biden and his son Hunter, according to the Times report.

David Jolly, who represented a Florida district from 2014 to 2017, said the GOP-controlled Senate must now call Bolton as a witness during the president’s impeachment trial. And if they don’t, he argued, they’re guilty of a cover-up.

Pretty simple. If a Senator now votes no on calling Bolton to testify they're knowingly engaging in a cover-up. — David Jolly (@DavidJollyFL) January 26, 2020

Jolly, a consistent Trump critic, quit the Republican Party in 2018 over its support of the president.