On Tuesday night Julián Castro appeared at a rally in Brooklyn alongside Elizabeth Warren to express support for her bid for the Democratic presidential nomination. It’s no surprise that in a field of candidates that’s grown increasingly male and white, he opted to throw his support behind the leading female candidate.

When Mr. Castro ended his campaign last week, just a little under a year after he made a bilingual announcement in his hometown San Antonio with mariachis, accent-marked campaign signs and a Selena soundtrack, it confirmed that Latino voters have never been a unified voting bloc.

He was the first candidate to release an immigration plan that offered a road map for decriminalizing immigration. His bold substantive plan was a departure for a party that has engendered mistrust and skepticism about whether traditional Democrats are serious advocates for the Latino community.

And yet, he never really had a shot. Mr. Castro ran a small campaign that lagged behind in fund-raising and failed to get traction. The former Secretary of Housing and Urban Development in President Barack Obama’s administration consistently trailed Bernie Sanders, Joe Biden and other candidates, including Ms. Warren, in recent Latino voter polls.