Democratic presidential candidate Julián Castro lost one of his congressional endorsements Sunday, with Texas Rep. Vicente González switching to support former Vice President Joe Biden.

González was one of three Texas representatives who endorsed the former HUD secretary, along with Castro's twin brother, Rep. Joaquin Castro, and Rep. Colin Allred. González announced his endorsement for Julián Castro in March, saying at the time, "I know firsthand his passion for expanding opportunity for the Latino community, people of color, and historically disenfranchised communities, as well as his unparalleled dedication to building a bench of dynamic Democratic candidates in Texas and nationally."

González announced his switch to CNN's Jake Tapper on Sunday morning, saying: "I think at this point in time we need to narrow the field and unite as Democrats to defeat Trump in November 2020. And that is why I believe I'm moving my support to Vice President Joe Biden."

Castro and Biden went head to head at the third Democratic debate Thursday, with Castro going after the former vice president for his record on health care policy and for focusing so heavily on his ties to former President Barack Obama.

During one of the most dramatic moments of the debate, Castro accused Biden of wanting to "take credit" for Obama's accomplishments when it suits him but distancing himself from the former president on policies that have grown unpopular.

"I'm fulfilling the legacy of Barack Obama, and you're not," Castro said during the debate.

Biden is polling a the top of the Democratic field, and Castro is trailing well behind. González, in explaining his switch, noted that Castro was “polling in the low single digits.”