Sanders IS more popular than Hillary. Imagine how the Bernie bots are feeling about now. As others have pointed out, they believed in him. They DON'T trust Hillary. And when they stood beside him, he told them in essence, I know that I was defrauded. But hell, who cares? I'm endorsing the people who defrauded me. You should too. And he turned his back on them.
They are P.O.'d big time. We shall see if this is going to have an impact in the election.