Photo: Express-News File

WASHINGTON - U.S. Rep. Henry Cuellar is accustomed to winning big, averaging more than 70 percent of the vote in his last half-dozen general elections.

In eight terms, he has established himself as a distinctly moderate Democrat despite representing a south Texas district so blue that Hillary Clinton won in Webb County, his home, with 74 percent of the vote.

Now, responding to a primary challenge from the left, Cuellar has moved into full-hustle mode to protect his seat, gathering endorsements, dispatching paid canvassers and trumpeting his work in Congress.

His opponent: Jessica Cisneros, 26, the daughter of Mexican immigrants and an immigration lawyer who has drawn national backing, including an endorsement from presidential contender Elizabeth Warren.

In normal times, Cuellar’s flush campaign fund of $3.24 million and full-throated backing from House Speaker Nancy Pelosi and congressional Democrats’ political arm would seem sufficient for his re-election.

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But that is less certain now with progressive Democrats on the ascent in Washington and beyond, and Cuellar last week pushed out a lengthy list of local Democratic officeholders backing his re-election — 114 of them — and promises another such list in coming days.

Cuellar, 64, a senior appropriator on Capitol Hill, is touting his work on the newly negotiated U.S.-Mexico-Canada trade deal and trumpeting benefits of Democratic-engineered legislation to reduce prescription drug costs and give federal workers paid parental leave.

Last week, nearly three months before the primary, the Cuellar campaign dispatched 20 paid canvassers into the district, which stretches from the east side of San Antonio to his home base of Laredo and as far south as McAllen.

“We’re trying to be aggressive and get the word out that we’re running a very serious campaign and we’re going to have the foot soldiers in the form of local elected officials getting out our message and getting out the vote,” said Colin Strother, the lead consultant for Cuellar’s re-election drive.

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“What we want to do is help people understand that Twitter is not the real world,” Strother said. “Just because they have a really strong Twitter presence, that doesn’t change the reality on the ground.”

Social media is an active part of the Cisneros fundraising and messaging, which began early this year with the backing of Justice Democrats, a Tennessee-based organization pressing for the election of left-of-center Democrats.

Cisneros has drawn financial backing from an array of national organizations, aided by her endorsement from Alexandria Ocasio-Cortez, the first-term congresswoman from New York who has arrived in the political world with considerable buzz, and a well-known acronym, AOC.

(Cisneros has been quoted as saying: “I’m not trying to be the next AOC. I’m focused on being the next Jessica Cisneros, a fearless Tejana who speaks truth to power, because that is who my home district needs me to be.”)

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In an interview, Cisneros contended that the flurry of activity by Cuellar is a good sign for her campaign.

“The fact that he’s releasing this endorsement list, the fact that he’s all of a sudden feeling it necessary to send out canvassers, these are all things he hasn’t done in previous cycles. And for us that’s great, because it means that he’s finally taking us seriously,” she said.

Cisneros contends that Democrats have reason to reject an incumbent for being out of step with the district, even an incumbent with clout on the Appropriations Committee.

“We feel that we have had absentee leadership. When he shows up to places with a giant check, it doesn’t necessarily mean it’s stuff his office is putting forth. In reality, it’s been a lot of work for community organizations applying for grants. People get upset sometimes when he comes along with a check trying to take credit when actually it’s the work of people in our community,”

She pointed to Cuellar’s record of often voting in accord with President Donald Trump.

“This is a district that rejected Trump,” she said.

Cisneros last week proposed four town hall style debates. It’s unlikely she’ll get her wish.

Strother said in an email that Cuellar would have to cancel long-standing meetings for a debate that “would help her build her campaign and get attention that she’s not earning on her own merits.”

Asked if that’s a no, Strother replied: “It's not a no so much as it's not even a consideration. She is not a serious candidate.”