In 2016, when it was clear Hillary Clinton had the required number of delegates to win the nomination and Sen. Bernie Sanders had lost he refused to accept the result and pushed on to the convention continuing to incite his supporters against Clinton.
Let’s hope he will not do the same in 2020 to Joe Biden. There were times before when a losing candidate’s supporters threatened not to work for the nominee but in 2016 it was the candidate himself who made things worse.