In a race viewed as a bellwether for the Democratic Party's future, eight-term incumbent Rep. Henry Cuellar (D., Texas) defeated Jessica Cisneros despite an influx of out-of-state cash and high-profile endorsements for the progressive challenger.

Cuellar's campaign claimed victory early Wednesday morning, holding off Cisneros by a 52-48 margin. The result adds to an already rough night in Texas for Sen. Bernie Sanders (I., Vt.), who endorsed Cisneros in January. The Vermont democratic socialist was upset in the Lone Star state's primary by former vice president Joe Biden.

Cisneros's loss also comes as a blow to Rep. Alexandria Ocasio-Cortez (D., N.Y.) and the "squad" of far-left lawmakers that have rallied around her. The 26-year-old immigration attorney was handpicked to challenge Cuellar by Justice Democrats, the progressive group that backed Ocasio-Cortez and Rep. Ilhan Omar (D., Minn.) in 2018. The group painted Cuellar as "Trump's favorite Democrat," contrasting his pro-life stance and "A" NRA rating with Cisneros's liberal positions, emphasizing the challenger's support for Medicare for All, the Green New Deal, and a $15 minimum wage.

The race drew intense national attention. Cisneros landed endorsements from a who's who of progressive lawmakers and advocacy groups. Ocasio-Cortez, Sanders, Sen. Elizabeth Warren (D., Mass.), Rep. Ayanna Pressley (D., Mass.), and Rep. Pramila Jayapal (D., Wash.) all backed Cisneros, as did the environmentalist Sierra Club and abortion industry giants EMILY's List, NARAL Pro-Choice, and Planned Parenthood Action Fund. The Democratic Congressional Campaign Committee and House Speaker Nancy Pelosi (D., Calif.) endorsed Cuellar, with Pelosi calling for a "resounding victory" for the incumbent Democrat during a February campaign event.

The Cuellar campaign criticized Cisneros for her outside support, painting the progressive challenger as out of touch with south Texas. While the state's 28th Congressional District is deep blue—Hillary Clinton won it by 20 points in 2016—it boasts a large population of socially conservative Catholic and Latino voters. Cisneros and Justice Democrats cited Clinton's landslide victory as evidence of the district's support for progressive policies, a mistake according to Cuellar.

"I've been polling and my district is more moderate, conservative Democrats," Cuellar said in January. "I think an outside group that thinks that they know South Texas politics better than I do are going to find [that] out."

Cuellar outspent Cisneros, disbursing $2.2 million during the campaign compared to Cisneros's $1 million. The incumbent Democrat had $2 million on hand as of February 12, while Cisneros had just $296,000.

Both candidates benefited from heavy outside spending. The U.S. Chamber of Commerce and American Workers for Progress spent nearly $1 million on combined ad buys to back Cuellar, while the Voter Protection Project used a $250,000 contribution from the Congressional Hispanic Caucus to disseminate anti-Cisneros mailers. Texas Forward, a super PAC linked to EMILY's List, spent more than $1.2 million on ads supporting Cisneros.

Cuellar will now take on Republican challenger Sandra Whitten in November's general election. Whitten has raised less than $10,000 as of February 12.