Bernie Sanders endorsed Hillary Clinton. His supporters are absolutely livid.

Shortly before Bernie Sanders officially endorsed Hillary Clinton for president on Tuesday, Donald Trump tweeted that Sanders' supporters were "not happy that he is selling out." And indeed, one glance at the outpouring of bitter mourning and resentment on Sanders' Facebook page confirms that many of his supporters (or shall we say former supporters?) feel their candidate has betrayed them.

Sanders' endorsement of Clinton came despite his longstanding promise to not give up the fight. However, Sanders reassured his supporters that the two campaigns have come together recently to produce "by far, the most progressive platform in the history of the Democratic Party." But that may not be enough to ensure the Bernie bros are ready to follow Sanders into the Clinton camp.

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