Preston Ehrler/SOPA Images/Getty Images Rep. Alexandria Ocasio-Cortez, who endorsed Sen. Bernie Sanders' presidential bid on Saturday, is wading into primary races against House colleagues.

Rep. Alexandria Ocasio-Cortez announced Tuesday that she is endorsing Jessica Cisneros, an immigration and human rights attorney who has launched a progressive primary challenge against Rep. Henry Cuellar, a Texas Democrat.

The New York representative’s blessing is a major boost for Cisneros, who stands to benefit from Ocasio-Cortez’s national recognition and fundraising prowess. If she is successful, Cisneros, 26, would supplant Ocasio-Cortez, 30, as the youngest woman ever elected to Congress.

“Jessica is an incredible candidate who’s rooted in her community, who has served her community, who understands the working families of her community ― and she’s supportive of a progressive agenda,” Ocasio-Cortez told HuffPost in an interview.

“I want to be the shortest-lived ‘youngest congresswoman ever’!” she added with a laugh.

Ocasio-Cortez plans to leverage her sizable email list to raise funds for Cisneros on Tuesday, according to the representative’s campaign.

Cisneros welcomed Ocasio-Cortez’s support.

“We need people’s support to let the people of South Texas know that for the first time in over a decade, we have another choice,” she said in an interview with HuffPost. “It took 13 years for someone to step up to Henry Cuellar, but it’s been so great to have the support of people both within the district and across the country.”

It is famously difficult for primary challengers to unseat incumbent members of Congress. But Ocasio-Cortez’s endorsement ― the first for Cisneros from a sitting House member ― builds on existing momentum for the candidate, who is taking advantage of activist discontent with Cuellar’s record of opposition to gun regulation, abortion rights and immigration rights.

Cisneros fell just short of Cuellar, whom she calls “Donald Trump’s favorite Democrat,” in third-quarter fundraising, though she bested him in contributions that came from individuals, rather than PACs. Last Thursday, she picked up the influential endorsement of EMILY’s List, which backs female candidates supportive of abortion rights. And Sen. Elizabeth Warren of Massachusetts, a top competitor for the Democratic presidential nomination, came out for Cisneros in September, headlining a rally with her in Austin.

Colin Strother, a spokesperson for the Cuellar campaign, dismissed Ocasio-Cortez’s involvement in the race. “While our opponent continues to be focused on out of state endorsements, we remain focused on the voters in the district will actually decide this race in March,” Strother said.

Cuellar represents Texas’ 28th Congressional District, a gerrymandered swath that stretches from the San Antonio area down to Laredo and other cities on the border with Mexico.

Ocasio-Cortez said she is familiar with border towns in the district from her past work as an education organizer for the National Hispanic Institute. While she is sensitive to the concerns of moderate Democrats representing swing seats, Texas’ 28th is a case of a solidly Democratic district where the constituents are likely more progressive than their member of Congress, Ocasio-Cortez argued. She alluded to the fact that Hillary Clinton defeated Donald Trump there by 20 percentage points in 2016.

That disconnect between member and constituents “happens a lot more than people care to admit,” Ocasio-Cortez said. “I say that speaking from very personal experience. I now represent one of the most progressive districts in Congress. For decades our representation was quite regressive compared to where my community was at.”