WASHINGTON — Laredo immigration attorney Jessica Cisneros has raised nearly $500,000 since launching her bid to unseat longtime Democratic U.S. Rep. Henry Cuellar in June.

Cisneros, trying to tackle the well-known centrist Cuellar from the left, raked in more than $310,000 in the third quarter of the year, bringing her total raised to $459,000, according to her campaign. The haul is a sign that Cuellar, who’s been in office since 2005, may be facing his first real challenge in years. Cisneros’ campaign touted donations from 14,200 individuals — including nearly 3,000 Texans — who gave an average contribution of just over $32.

Cisneros, 26, has drawn national support. Democratic presidential hopeful Elizabeth Warren endorsed her last month, and her campaign is supported by Justice Democrats, a national progressive group that backed Rep. Alexandria Ocasio-Cortez’s insurgent bid to unseat a longtime Democratic congressman in New York. Justice Democrats said Friday that Cisneros’ fundraising has far outpaced the other primary challengers it has supported, including Ocasio-Cortez, who raised less than $60,000 in all of 2017.

“Everywhere I travel in the district, I hear from Texans who are fed up with Washington politicians serving corporate special interests and wealthy donors rather than our communities,” Cisneros said in a statement. “Our district deserves better, and that’s why I’m not accepting a dime from corporate PACs or lobbyists. In Congress, I’ll advocate for the values and concerns of real people down here in South Texas, not corporate special interests.”

Cuellar’s campaign manager, Colin Strother, said Cisneros’ haul “doesn’t change a single fundamental about this race.” Cuellar, he said, “understands the district and has a proven record of getting things done.”

Strother also said Cisneros is relying heavily on money from outside the South Texas district.

“Liberal senators in Massachusetts and Hollywood actresses might be supporting her campaign,” he said. “But nobody in the district is supporting her campaign.”

Cuellar, meanwhile, has plenty of money for his campaign. While he hasn’t released his third quarter fundraising figures, he had more than $3 million on hand in June, and Strother said the campaign has raised more than $1 million so far this year.

Cisneros hit Cuellar for pulling in contributions from political action committees.

“When you look through my filings on Oct. 15th, you won’t find money from outside corporate and Republican interests like GEO Group, Exxon, the NRA or the Koch Brothers,” she said. “I can’t say the same for my opponent.”

Cuellar is backed by the Democratic establishment, including House Speaker Nancy Pelosi, who said at the Texas Tribune Festival last month that she “absolutely, absolutely, absolutely, absolutely” supports him.

The GOP is also targeting Cuellar, 63, a member of the fiscally conservative Blue Dog Coalition who has supported the oil and gas industries. Tom Emmer, chairman of the National Republican Congressional Committee, recently called him the most vulnerable Democrat in Texas. The NRCC pounced on Cisneros’ fundraising haul, saying in a statement that “Henry Cuellar is going to need to call in the big guns in his party.”

The 28th Congressional District stretches from Laredo to San Antonio’s East Side and includes part of the Eagle Ford Shale oil play. It’s a district Cuellar has been able to hold on to with little trouble. He drew 90 percent of the vote against his last primary challenger, William Hayward, a government contractor who deemed himself a “conservative Christian” and ran in other races as a Republican. It was Cuellar’s first primary challenge in a decade, and he won the one before that — against two challengers in 2006 — by 13 percentage points.

Cisneros is one of several progressive hopefuls who have jumped into Democratic primaries in Texas, arguing that a key to turning the state blue will be reaching voters who have not made a habit of voting in the past — especially young and minority voters, who they believe can be energized by an unflinching progressive message.

ben.wermund@chron.com