Bernie Sanders endorsed Hillary Clinton two weeks ago — and we just saw a dramatic demonstration that not all of his supporters are particularly happy about it.

While addressing a rally of Sanders supporters in Philadelphia on Monday afternoon, the senator said, "We have got to defeat Donald Trump, and we have got to elect Hillary Clinton and Tim Kaine" — and he was met by a chorus of boos.

.@BernieSanders booed telling supporters to help elect Clinton: "This is the real world that we live in." https://t.co/8jV2wUWtiK — ABC News Politics (@ABCPolitics) July 25, 2016

The loud booing continued for some time. "Brothers and sisters. This is the real world that we live in," Sanders said. "Trump is a bully and a demagogue. Trump has made bigotry the cornerstone of his campaign."

Sanders will speak in primetime at the Democratic National Convention tonight.