Calls are increasing for the Senate to subpoena former national security adviser John Bolton to testify in the impeachment trial, after a bombshell report indicated that President Donald Trump tied Ukrainian military aid to investigations on the Bidens during conversations with Bolton.

The New York Times on Sunday reported that a manuscript of Bolton’s new book, circulated at the White House for review, states that Trump told his then-national security adviser the hold on Ukrainian military aid would not be released until the Biden investigations were announced. It’s an explosive revelation that contradicts Trump’s legal defense in the ongoing impeachment trial.