Julián Castro, who dropped out of the 2020 presidential race last week, endorsed Elizabeth Warren on Monday.

"There's one candidate I see who's unafraid to fight like hell to make sure America's promise will be there for everyone, will make sure that no matter where you live in America or where your family came from in the world — you have a path to opportunity, too."

Why it matters: It's one of the first high-profile endorsements from a former presidential contender this cycle — and it's significant because Castro is widely viewed as a leading vice presidential pick for the eventual nominee.

Our thought bubble, via Axios' Alexi McCammond: Castro and Warren have been pretty close throughout the primary, and his endorsement reflects that bond they’ve shared.

They will be campaigning together, and he will make solo appearances without her as well.

If Warren has to be pulled from campaign trail to participate in the Senate impeachment trial, Castro will be a crucial surrogate during that time.

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