Democratic presidential candidate and U.S. Sen. Elizabeth Warren on Monday endorsed progressive immigration attorney Jessica Cisneros in her primary campaign to unseat U.S. Rep. Henry Cuellar, D-Laredo.

“The people of Texas’ 28th district are ready for systematic change and deserve a Democrat that will be on the side of working people; not the side of big money and obstructionist Republicans,” Warren said in a statement released Monday. “I believe Jessica Cisneros is that fighter. As an immigration lawyer and daughter of small business owners growing up on the border, Jessica knows our diversity is our strength and that when progressives are unapologetic about our values and who we’re in this battle for, we win. It’s time Texans had a champion in Congress who does just that. I’m proud to support Jessica.”

Cisneros, who is 26 years old, a Laredo native and backed by the progressive Justice Democrats organization that also supported the New York City progressive U.S. Rep. Alexandria Ocasio-Cortez in her 2018 upset primary win, said Warren’s support “proves we have the momentum” to bring new representation to the congressional district that stretches from Laredo to Mission.

“I’m so proud to receive this endorsement from Senator Warren, who has dedicated her career to fixing our corrupt political system and fighting for working families like mine,” Cisneros said in a statement. “Our district deserves to be represented by a true Democrat who will work in Washington to improve the lives of her constituents, not corporate donors. Senator Warren’s support demonstrates that we’re building the momentum we need to bring real change to South Texas.”

The Cuellar campaign responded on Monday.

“We told you the outside special interests were coming to take away local jobs,” the Cuellar campaign wrote on Twitter. “Elizabeth Warren and our opponent share an agenda that would kill over 108,000 jobs in our region. I’m fighting back.”

Monday’s endorsement marks more high-profile attention on the race, after the June launch of Cisneros’ campaign that drew some national attention at the time. Justice Democrats had raised its profile following Ocasio-Cortez’s 2018 victory, and Cisneros was the first candidate the progressive group recruited and backed in this election cycle.

“Our congressman claims to be a Democrat, but he’s voted with Trump nearly 70% of the time,” Cisneros said in her campaign launch video, also criticizing Cuellar for receiving an “A” rating from the National Rifle Association and for accepting sizable donations from private prison groups.

Colin Strother, Cuellar’s campaign spokesman, said on the day of Cisneros’ launch that South Texas does not align with the views of a group like Justice Democrats.

“We feel like the congressman votes the values of his district and he knows it a little better than a New York-based special interest group like Justice Democrats,” Strother said, also criticizing the policy agenda of the Justice Democrats — that of pushing the Green New Deal, gun reform and abolishing Immigration and Customs Enforcement — as job-killing for tens of thousands of people in the district.

“This isn’t the Bronx; this is the border,” Strother added, referencing Ocasio-Cortez’s congressional district.

The Justice Democrats zeroed in on Cuellar earlier this year, identifying him as what they believe is a flimsy Democrat whose time in Congress — he took office in 2005 — needs to end. Cuellar, at a luncheon this spring in McAllen, responded to the threat of a primary challenge.

“One of the things that we see in Washington, D.C. is there’s extremes,” Cuellar said in late May. “And those are the ones that you usually hear about. But there’s a lot of us in the middle that want to get the job done.”

Cuellar’s bipartisanship, however, took a hit late last week, when the Trump administration announced 52 miles of border wall coming to Laredo. Nate Silver, who heads the data and analysis website fivethirtyeight.com, said that Warren’s endorsement “made sense” considering that “Cuellar has by far the most pro-Trump voting record of any Democrat in Congress, relative to his district.”

In Pharr late last month, Cuellar spoke on a panel alongside his frequent bipartisan collaborator in Congress, U.S. Sen. John Cornyn, R-TX. The two discussed cross-border trade, its benefit to border communities and its favorable economic impact on Texas.

“I don’t want to say too many nice things about Congressman Cuellar,” Cornyn told reporters after the event. “I don’t want to hurt his primary race. So let me just say, he’s a good man, and somebody I look forward to working with on a regular basis.”