In an interview on Rachel Maddow’s MSNBC show, Sen. Elizabeth Warren of Massachusetts endorsed Hillary Clinton’s campaign for president, saying, "I’m ready to get in this fight and work my heart out for Hillary Clinton to become the next president of the United States and make sure Donald Trump never gets anywhere close to the White House."

Warren’s core point is that Trump is really bad, other Republicans are really bad, Clinton is de facto the nominee already, and it’s time for progressive-minded people to come together and try to win. She didn’t stint on praise for Sanders, saying he "brought millions of people into the Democratic Party" with an inspiring message that was "about millions of people who work hard every day and just keep getting slammed."

Beyond the minimum case for Clinton, she vouched for her progressive credentials, calling her a "fighter" who's going to be "willing to throw a punch" in a way that Democrats don't always do.

Why Warren’s endorsement matters

An early endorsement of Clinton by Warren could have helped the former secretary of state in the primaries. This late in the process, it can’t possibly make a difference, since Clinton has already won. But where it can make a difference is in persuading Bernie Sanders's supporters to get over their campaign season anti-Clinton feelings and hop on board.

That’s because, like Barack Obama and Joe Biden, Warren is very popular with Sanders supporters, including Sanders supporters who say they won’t vote for Clinton in the general election.

And while Warren’s support is less significant than Obama's in this regard, it carries more weight than Obama’s with a small but potentially influential group of thought leaders and ideological activists.

Anti-Clinton Bernie fans who also like Obama are basically confused about where the various politicians stand. Warren is different. Ideologically speaking, she’s considerably closer to Sanders than she is to Clinton or Obama. Specifically, she is the most prominent enemy of Wall Street and big banks in American politics, and if she says progressives should get over Goldman Sachs speeches and back Clinton, that carries weight.

Not everyone is happy about it

Of course, endorsements are a two-way street. While Warren may persuade some progressives to accept Clinton as a clearly superior choice in the general election, others may merely be convinced that this proves Warren is a neoliberal sellout.

Already her Facebook page is full of hostile comments from angry Sanders backers:

That said, the post has more than 6,000 shares on Facebook, suggesting that, as usual, internet commenters probably aren't representative of the views of the general public.

Bernie Sanders is going to drop out soon

Warren’s endorsement also underscores the fundamental reality that Sanders isn't really going to fight all the way to the Democratic National Convention.

The theory of the convention fight was that he would use the weeks between now and the convention to argue to superdelegates that he is a better anti-Trump candidate in the fall. The reality is that superdelegates are moving in the opposite direction. Formerly neutral superdelegates — including ones like Warren who are ideologically sympathetic to Sanders — are lining up behind Clinton. Sanders has the option of ignoring the reality that he is losing support, but this will only make him new enemies and divide his supporters.

It now appears that Sanders will stay in the race at least through Tuesday’s primary in DC, but he is definitely going to lose there and fall even further behind in pledged delegates.