Centrist U.S. Representative Henry Cuellar seeks to hold off progressive challenger Jessica Cisneros on Tuesday in a high-profile south Texas Democratic primary battle that illustrates sharp dividing lines over immigration and abortion rights.

The election in a district along the U.S.-Mexico border is the third contest between Cuellar, who has held the seat since 2005, and Cisneros, a 28-year-old attorney who failed to unseat him in 2020 but forced him to a runoff in the state's March primary this year.

The race took on new urgency in recent weeks after a leaked opinion indicated that the Supreme Court could overturn a 1973 ruling that legalized abortion nationwide.

Cuellar, 66, is the lone House Democrat to oppose abortion rights, and abortion-rights groups have spent at least $160,000 to bolster Cisneros's campaign.

Cuellar has said Cisneros would risk public safety and hurt the local economy by cutting law enforcement funding in a district where many voters work for border patrol agencies.

Cisneros has since distanced herself from her previous call to eliminate U.S. Immigration and Customs Enforcement.

Political analysts have said a Cisneros win could threaten Democrats' chances to hold the seat in the Nov. 8 election, when Republicans hope to win control of the House of Representatives.

But Cuellar's strength in the general election shouldn't be a foregone conclusion, said Joshua Blank, research director of the Texas Politics Project at the University of Texas in Austin.

"The reality is that Cisneros has come very close to unseating Cuellar twice at this point," Blank said. "If he can't defeat Cisneros, then I think the logic underlying that should come into question."

Cisneros has benefited from increased name recognition and an FBI investigation that saw raids on Cuellar's home and office.

Financial disclosures on Friday showed she has out-raised him by almost $1.4 million, and has around $400,000 more cash on hand than Cuellar.

The race is one of several midterm primary battles Tuesday between incumbent House Democrats and progressive challengers.

In Oregon, Jamie McLeod-Skinner looks set to oust moderate incumbent Kurt Schrader, while in Pennsylvania progressive Summer Lee has a slight lead over Steve Irwin. Other progressive challengers like Nina Turner in Ohio have lost.