WASHINGTON (CBSDFW.COM/AP) — Former San Antonio Mayor and Barack Obama housing secretary Julián Castro ended his run for president last week and today he’s endorsing Elizabeth Warren’s 2020 presidential bid.

In a video posted to social media, Castro said the Massachusetts senator is “the most qualified, best-equipped candidate to win the nomination” and defeat President Donald Trump.

In the video featuring the two former 2020 White House rivals, Castro tells Warren, “No one is working harder than, you.” The pair had remained friendly during months of campaigning.

Castro dropped out of the presidential race on January 2. The Iowa caucuses that kick off the Democratic primary are less than a month away.

Warren’s campaign announced minutes after the endorsement that Castro will appear with Warren at a rally Tuesday evening in New York City.

Democratic presidential hopefuls (L) former Secretary of Housing and Urban Development Julian Castro and Massachusetts Senator Elizabeth Warren chat after participating in the first Democratic primary debate of the 2020 presidential campaign. (credit: Jim Watson/AFP via Getty Images)

In a statement, Castro said the 3-minute endorsement video explains why “Elizabeth and I share a vision of America where everyone counts. An America where people — not the wealthy or well-connected — are put first.”

Warren has for months polled among the still-crowded primary’s front-runners in Iowa and nationally, along with former Vice President Joe Biden, Vermont Sen. Bernie Sanders and former South Bend, Indiana, Mayor Pete Buttigieg. All four enjoyed strong fundraising through the end of 2019, further evidence the primary could be a long, drawn-out battle.

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)