WASHINGTON — The primary challenger to Rep. Henry Cuellar, D-Laredo, picked up a high-profile, out-of-state endorsement Tuesday from Rep. Alexandria Ocasio-Cortez, the Bronx Democrat who has made major waves in her inaugural term in Congress.

Ocasio-Cortez hailed Jessica Cisneros, a Laredo attorney, as someone who is “deeply connected to the problems and struggles facing her community.”

“The people of South Texas deserve a Democrat like Jessica who is going to fight for real people, not big corporate donors like the Koch Brothers, GEO Group, and Exxon,” the New Yorker said in a news release, referring to some of Cuellar’s campaign contributors.

Happy to take the title of Youngest Member of Congress from ya, @AOC! 😉🙌 https://t.co/X9lCfK0rey — Jessica Cisneros for Congress (@JCisnerosTX) October 22, 2019

It’s uncommon for a member of Congress to endorse the primary opponent of a lawmaker who serves in the same political party.

But South Texas is proving to be a showcase for a deep ideological schism within the Democratic Party as progressive groups and leaders have set their sights on Cuellar, a senior lawmaker who is one of the most conservative Democrats in Congress.

Just last month, White House hopeful and Massachusetts Sen. Elizabeth Warren likewise backed Cisneros, saying that the “people of Texas’ 28th district … deserve a Democrat that will be on the side of working people, not on the side of big money.”

Cuellar, though, has heavyweight support of his own.

House Speaker Nancy Pelosi, while not making an official endorsement, said last month at the Texas Tribune Festival in Austin that she “absolutely, absolutely, absolutely, absolutely” supports Cuellar and is “very, very proud” of her fellow Democrat’s work in Congress.

And Cuellar on Tuesday brushed aside Ocasio-Cortez’s move, telling The Hill that he’s “not at all” worried about it.

Cuellar campaign spokesman Colin Strother also added that “the people of the 28th district are going to decide this race, not out-of-state PACs or celebrities.” He said the campaign is “very confident that we’ve got a better barometer for the attitudes of the district.”

“The congressman’s voting history tracks very closely to the values of the district,” he said.

Rep. Henry Cuellar, D-Laredo, said Tuesday that he's "not at all" worried about Rep. Alexandria Ocasio-Cortez endorsing his primary challenger. (Tom Brenner / Getty Images)

It’s unclear what kind of sway Ocasio-Cortez might have in South Texas, though her national profile is sure to boost Cisneros’ fundraising efforts.

The freshman lawmaker has earned substantial attention in her early tenure by proposing sweeping policy proposals like the Green New Deal; wielding a Twitter account with 5.6 million followers; and clashing with Republicans in Washington and beyond.

Cisneros on Tuesday said she was eager to take from Ocasio-Cortez the “title of Youngest Member of Congress.”

“Though the Bronx and South Texas are worlds apart, both deserve leaders who will stand up to big corporate interests to fight for a living wage and health care for every American,” she said in a news release.

The challenger raised about $465,000 through the end of September, according to the latest campaign finance reports. That sum is a lot for a political newcomer, but it’s still less than the $1.1 million Cuellar has raised in the first nine months of this year.