https://www.washingtonexaminer.com/news/joe-biden-visited-ukraine-six-times-in-eight-years-while-vice-president
It later emerged that in private he told Poroshenko that the $1 billion guarantee was linked to those reform efforts, including removal of Viktor Shokin as prosecutor general.
Critics have tried to suggest that Biden was motivated by Shokin’s investigation into Burisma, which counted his son Hunter on its board. But the European Union, the International Monetary Fund, and other allies had the same objective, and Biden was repeating U.S. policy that had been set out by Washington’s ambassador to Kiev in the preceding months and was briefed by White House staff just ahead of the trip.