This is evidenced by a printout of the well-publicized phone call that prompted Democrats to initiate a civil lawsuit against Trump.
Trump told his Ukrainian colleague that he had heard that Biden halted an investigation into suspected corruption in the Ukrainian energy company Burisma Holdings, which was due to Biden's son Hunter serving on the company's board until April this year.
"Biden walked around joking that he stopped the prosecution so if you can watch it ... it sounds awful to me," Trump said according to the printout.
According to information leaked to the media, Trump used military aid pledges to put pressure on Zelensky. It has not yet been ascertained if such a thing occurs in the transcript of the call.
Trump himself has admitted that he discussed Biden with Zelensky but denies that he made any connection to military aid. On the other hand, he has confirmed that he ordered a freeze of close to 400 million aid to Ukraine a few days before the telephone call.