Former National Security Adviser John Bolton was made to squirm by one of his predecessors Wednesday night when Susan Rice took him to task for his failure to testify in President Donald Trump’s impeachment trial. Bolton and Rice—who served as national security adviser under former President Barack Obama—shared a stage at Vanderbilt University. Rice repeatedly criticized Bolton for not testifying before the House of Representatives, despite reports that his upcoming book will contain damning claims that Trump tied Ukraine military aid to the investigations that he wanted. “I can’t imagine withholding my testimony with or without a subpoena,” Rice reportedly told Bolton. “I would feel like I was shamefully violating the oath that I took to defend the Constitution against all enemies foreign and domestic.” According to the Vanderbilt Hustler student newspaper, Bolton said: “I said I would testify if subpoenaed. My position is exactly the same as Joe Biden.” Rice is reported to have hit back: “Except Joe Biden didn’t have firsthand knowledge about what transpired with Ukraine.”