This year, he’s up against a challenge from the left: 26-year-old immigration attorney Jessica Cisneros. Cisneros grew up in Laredo, and was practicing law in New York when she was recruited by Justice Democrats to run against Cuellar. That's the same group that backed Rep. Alexandria Ocasio-Cortez, who defeated longtime Democratic incumbent Joe Crowley who had held his seat for 20 years.

Cisneros is running on a progressive platform of Medicare for All, a $15 minimum wage, and one of Ocasio-Cortez's signature initiatives, the Green New Deal.

“I think there's this myth that South Texas is very conservative and that is a myth that people like Cuellar are benefiting from,” Cisneros told VICE News. “For the past 12 years, he hasn't had a primary challenger.”

Cuellar describes Cisneros’ platform as being “completely against the district,” calls Justice Democrats “socialists,” and argues that they are attempting to “purify” the party.

“My job as a congressman — as opposed to some people — is it's not to go to Washington and make political statements,” Cuellar told VICE News. “I want to be productive. I want to make sure that I can produce for my district. I'm a Democrat but I'm not going to put party before people.” Asked why he is a Democrat, Cuellar cites issues like education and health care.

The question of where this congressional district truly is ideologically is hard to answer, in part, because the district is notoriously difficult to poll.

This is not the first time Cuellar and Cisneros’ paths have crossed: five years ago, she was his intern. She tells a story of Cuellar cautioning her against beginning her political career by running for congress. Cuellar refutes the story, calling it, “Absolutely not true.”

Beating Cuellar won’t be easy, especially given the disparity in their campaign resources. At the last FEC filing, Cuellar had more than $3 million cash on hand. Cisneros had $125,466.79. But Cisneros claims she’s already pushing him to the left, citing a recent vote the congressman took in support of raising the minimum wage. Cuellar laughed and dismissed that claim. “If it rains I hope she gets credit for that too,” he told VICE News.