President Trump tied military aid to Ukraine to investigations into former Vice President Joe Biden and his son Hunter, former National Security Adviser John Bolton writes in an unpublished manuscript, according to The New York Times. The manuscript offers a look at Bolton might say if called to testify in the president’s impeachment trial, the Times reports. The former national security adviser has offered to testify if subpoenaed, over the White House’s objections. According to the Times, Bolton also writes in the manuscript that Secretary of State Mike Pompeo believed the president’s personal lawyer Rudy Giuliani could have been working in Ukraine for clients other than Trump. Bolton also reportedly writes that Pompeo said privately that Giuliani’s allegations that the U.S. ambassador to Ukraine was corrupt were unfounded.