On the other side, Cuellar has raised $1.8 million and entered the final weeks with a $2 million war chest — as well as the backing of House Speaker Nancy Pelosi and Majority Leader Steny Hoyer, both of whom have stumped for him in the district. Alongside them are some odd bedfellows for Democrats: the U.S. Chamber of Commerce and the billionaire Koch family’s LIBRE Initiative Action, a Hispanic-focused libertarian group that hailed Cuellar as “the model of what an effective congressman should look like.”

At a "meet-the-candidate" event inside a Laredo strip mall tavern, Cisneros acknowledges that a climate-focused pitch in the Eagle Ford Shale region that has been at the center of the boom in U.S. oil and gas production is a hard sell. But instead of calling for a phase-out of fossil fuels, she's adapted the Green New Deal message to the district’s culturally conservative voters.

Rep. Henry Cuellar. | Alex Wong/Getty Images

“I can’t go to someone’s door and ask them, ‘What do you think about the Green New Deal?’ because they have no frame of reference as to what that means,” Cisneros said. “We’re unpacking what it means: Investment in solar and wind and infrastructure more than anything, and what jobs that could create for the people here. Jobs are what excites people.”

Texans overall are more skeptical about climate change than most of the nation, though Democrats there are more in line with the 90 percent of their party in the entire country who think the federal government is doing too little to fight the problem.

And Cisneros’ pitch also comes second to her Medicare for All message, which is designed to appeal to voters in the district where nearly a quarter lack health insurance.

Cuellar hasn’t faced a serious challenge since he was first elected in 2004. But the support his opponent has drawn — and the nearly 17,000 newly registered voters in Webb County — have gotten his attention.

“There’s two ways to run — unopposed or scared,” Cuellar said in an interview. “I’m working it very, very hard. I don’t take anything for granted.”

Cuellar has been flooding local airwaves with more ads and sending more mailers than in any of his recent elections. He has attacked Cisneros, a Laredo native who passed the bar for immigration law in New York, as out of touch with residents — and an opponent of oil and gas drilling.

Progressive Democrats bristle at Cuellar’s votes in favor of a funding for a border wall or against sweeping labor rights legislation. And they slam him as “Big Oil’s favorite Democrat," since Halliburton, Conoco, Koch Industries and other industry giants have given nearly $800,000 to his campaign this cycle alone, according to the Center for Responsive Politics.

That’s brought out big green support for Cisneros from the Sierra Club and League of Conservation Voters, as well as the youth-oriented Sunrise Movement that’s been one of the most vocal advocates of the Green New Deal.

“If this is an important race for the Koch network, then it’s an important race for us too,” said Evan Weber, political director of the Sunrise Movement. “If they lose him, that might be a sign they’re losing the Democratic Party on the whole.”

The Justice Democrats, who have funded primary challenges to six Democratic candidates this election, see the fight as crucial to enacting aggressive climate change policy.

“In order to win a Green New Deal and strong climate policy, you have to take on members of the Democratic establishment, as well as those who are doing the bidding of oil corporations,” said Justice Democrats’ communications director, Waleed Shahid. “There are forces within our own party that will stop strong climate legislation from ever happening. You can try to persuade them or you can try to defeat them. And I think you’ll see a little of both.”

Progressives see the outside support for Cisneros as a clear indication the race will be competitive. The Sunrise Movement plans to continue phone banking for Cisneros through Election Day, a technique they they argue is more effective than door knocking in a district where many residents lack legal status.

But Scott Reed, the senior political strategist for the Chamber of Commerce, which has disclosed spending $200,000 on ads mentioning the incumbent, said South Texas is a far cry from the New York district that Ocasio-Cortez won.

“This is a classic Texas free enterprise versus New York City socialism race,” Reed said. “Justice Dems is a movement looking for something to do, and we just think they picked the wrong place to make this a referendum on their leftist agenda.”

Though no public polling on the race has been released, some experts say Cuellar could be vulnerable to the momentum that progressive candidates like Sanders or Ocasio-Cortez have tapped into.

“This is going to be his first real hard election in a while,” said political science professor Henry Flores at San Antonio’s St. Mary's University. “If he’s not careful, he may be caught off guard on this one, because this is a classic example of an insurgent grassroots campaign that’s putting a nose to the grindstone and grinding it out.”

Cuellar is betting on name recognition in a district where the biggest city already has a street named after him, and he’s touted his role in bringing the first wind farm to South Texas. Still, with oil and gas drilling bringing thousands of jobs and millions of dollars to his district, he doesn't think the type of transition away from fossil fuels Cisneros is advocating appeals to locals.

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“I’m going to make sure that we protect the energy industry in my district,” Cuellar said.

That pull, however, may not be as strong as it was a few years ago, when the oil and gas industry’s presence in the district was greater.

Cotulla, a small town just over the northern edge of Cuellar’s district, became a boomtown in the middle of the last decade because of its proximity to the Eagle Ford Shale. Workers flocked to the city to run the drilling rigs and lay pipelines in the area. A town with a population of fewer than 5,000 people soon became home to two dozen large hotels. Sales tax revenue gushed to $3 million at its peak in 2013, a city official said, eight times what it had been before the boom.

Those days are over, though. Even though big rigs still kick up dust going through town, the workers have mostly moved on to other projects after finishing the wells. One hotel went bankrupt, others have changed owners and tax revenue has shrunk to a third of its peak. City blocks that had once housed drilling service companies are vacant and boarded up.

The only building with the lights on in its historic downtown on a morning was the one housing city hall. There, Cotulla City Administrator Larry Dovalina, a self-described personal friend of Cuellar, describes himself as a conservative Democrat who wouldn’t vote for a presidential candidate in 2020 if the party nominated anyone besides former New York Mayor Mike Bloomberg.

Even with the downturn, the Texas oil patch is not ready for a Green New Deal, Dovalina said during an interview in his office. “The loss of jobs would devastate the area,” he said.

A two-hour drive south, the small city of Zapata abuts the U.S.-Mexico border. The town is mostly supported by farming and a declining natural gas industry. Resident Eva Linda Paredes hasn't heard of Cisneros, but says she thinks Cuellar is a distant relative and believes both families emigrated from the same Mexican town generations ago. She doesn’t know if she would vote for him, since she doesn’t think he’s done enough to help the economically struggling area.

Paredes said she receives $100 every three months in royalty payments for natural gas produced on land she owns, but “it used to be more,” she says. “I think right now, everything is going down.”