Elizabeth Warren is endorsing Hillary Clinton. Her progressive fans say she's betrayed them.

Elizabeth Warren is reportedly set to endorse Hillary Clinton, the presumptive Democratic nominee, for president tonight. And Warren's progressive Facebook fans are not taking it well. At all.

Warren hasn't made an official announcement yet, but the comments section on her latest Facebook post, promoting an anti-Trump speech Warren is set to give Thursday night, has erupted with rage and disappointment from Bernie Sanders supporters.

And the negative comments were outnumbering comments of support by a big margin:

All the necessary caveats go here, of course — a tight, emotional primary race just ended, and people who talk on the internet about politics are not representative of voters as a whole.

History suggests that most Sanders supporters will eventually come around. As the 2008 primaries ended, 25 percent of Democrats said they were either dissatisfied or angry with the nomination of Barack Obama, according to a Washington Post/ABC poll from June 2008. Most Democrats thought Obama should pick Clinton as his running mate, and 24 percent thought that if he didn't, she should stage a fight at the convention.

None of that held Obama back in the general election. Clinton supporters showed up and voted. And 88 percent of Democrats told the Washington Post and ABC in a May poll that they think the party will eventually unite behind Clinton. Clinton is less popular with Democrats now than Obama ever was, but she’s running against Donald Trump, and she’s still more popular than he is.

Still, 2016 has shown that just because an election played out one way in the recent past doesn’t mean it’s always going to continue in that vein. And the fact that Sanders supporters are willing to turn on Warren — a hero to the progressive movement — shows just how deep the wounds of the past few months remain.

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