Why is this news? Because, according to Dave Weigel, of the 15 Democrats who have dropped out of the race, only three so far have endorsed former opponents and two of those (Mike Gravel and Tim Ryan) were complete nonfactors. Castro’s is the first potentially meaningful endorsement by an ex-candidate.

It’s a surprise at first blush since Warren’s the one member of the top tier who’s lost meaningful ground in polling over the past few months. She’s tied for third in a new national survey with Mike farking Bloomberg, for cripes sake, and is now eight-ish points or so out of the lead in Iowa and New Hampshire according to CBS’s latest. Castro’s betting on a horse that seems to be fading — and yet, I think it’s a smart longshot play. Clearly he’s angling for the VP slot here and just as clearly he seems to have eyed Warren as the potential nominee who’s most likely to choose him, and not just because they’ve been friendly on the trail throughout. He’s held his fire against her from the start:

Castro endorsing Warren shouldn't come as a surprise, since he spent time attacking other non-Warren Dems.

He went after O'Rourke, Biden and Buttigieg in the Dem debates.

And he used his Twitter feed to blast Pete.

Castro never once went after Warren. https://t.co/dPCL5O3ruq

— Mark Murray (@mmurraypolitics) January 6, 2020

Biden/Castro, Sanders/Castro, and Buttigieg/Castro tickets all have an obvious problem in a party that depends heavily on support from women voters and which only three years ago crowned the first major-party woman nominee in American history. A woman virtually *must* be on the ticket next year, and maybe on every Democratic ticket thereafter. There’s only one woman remaining in the top tier right now, who also happens to be white and will therefore be looking for a running mate who’s male and nonwhite for optimum demographic balance. Enter Julian Castro, who proved at the debates per the tweet above that he’s willing and able to play the traditional VP role of attack dog for her against the opposition.

Endorsing Warren early, at a moment when she looks like an also-ran, will doubtless earn respect and gratitude from her and her team, further positioning him for a VP reward next summer if she surges back to win the nomination. The timing is good for both of them in another important way too — Warren’s about to be imprisoned in the Senate for weeks while Trump’s impeachment trial plays out in Washington. Until this morning, that meant she’d be off the trail in Iowa and New Hampshire and without any prominent surrogates. As of this morning, she now has a well-known former candidate ready to step in without missing a beat and make the case for Warren 2020.

Granted, ideally she’d have better options than a guy who recently told Iowa and New Hampshire that they’re too white to be hogging the early-state primaries. But at this point she’ll take what she can get.

I’m curious to know when, exactly, this endorsement was arranged. Castro dropped out of the race just four days ago, yet there he is in the clip below at Warren’s home enjoying coffee talk at her dining-room table. She was also quick to lament his departure from the race on Twitter last week:

Thank you @JulianCastro for being a powerful voice, for proposing bold and progressive plans, and for using your campaign to help people who need it now. You made this race stronger—and you will continue to be a leader in our party and our country for many years to come. pic.twitter.com/SWlsDC9HcS

— Elizabeth Warren (@ewarren) January 2, 2020

Did they record the ad below before he formally withdrew? His candidacy’s been dying for a long time. It makes sense that they’d coordinate to release the news that he was dropping during the slow holiday news cycle, when no one was paying attention, and then come roaring in with the announcement of his endorsement as soon as post-holiday business reopened on Monday morning.

One other virtue of this endorsement for Castro: Backing the lone plausible woman nominee left in the race boosts his woke cred, which he cultivated carefully on the trail this year. He’s obviously planning to run for president again someday. When he does, he’ll get the same question every male Democratic presidential contender will get for the foreseeable future, namely, “Why shouldn’t we nominate a woman instead?” Castro’s answer is now ready-made. “I’ve always believed in nominating the best candidate regardless of gender,” he’ll say, “and I proved it when I supported Elizabeth Warren in the 2020 primary.” Julian plays the long game.

Today I'm proud to endorse @ewarren for president.

Elizabeth and I share a vision of America where everyone counts. An America where people⁠—not the wealthy or well-connected⁠—are put first. I'm proud to join her in the fight for big, structural change. pic.twitter.com/xDvMEKqpF3

— Julián Castro (@JulianCastro) January 6, 2020