Bernie Sanders won the presidential nomination, but he was cheated out of it by the Democratic National Committee which is the operating body for the Democratic Party.
They helped Hillary win the nomination by combining vote miscounts and appointing super delegates whom no one elected to vote for Hillary. So, she won this nomination illegitimately. All of Bernie Sanders’ supporters know that.
They have turned against Hillary, and it is unlikely that many of them will vote for Clinton. The Democratic National Committee said:
“Who do they dislike more than Hillary? The Russians”, as they’ve been demonizing the Russians for the last 3-4 years.