Two of the most powerful Democrats in Congress are making their support for U.S. Rep. Henry Cuellar, D-Laredo, crystal clear as he faces a spirited primary challenge from his left.

During appearances this weekend in Austin, including at The Texas Tribune Festival, House Speaker Nancy Pelosi and Cheri Bustos, the head of the House Democrats' campaign arm, lavished praise on Cuellar, and Bustos said more than once that she was not concerned about his reelection prospects.

"Henry Cuellar knows that district like the back of his hand," Bustos said Saturday at a briefing for reporters. "I completely support him. ... He has very good relationships with the vast majority of his colleagues — who are supportive of him — and I think he'll be fine."

Cuellar is being challenged by Laredo attorney Jessica Cisneros, who has the backing of Justice Democrats, the progressive group well-known for helping elect freshman U.S. Rep. Alexandria Ocasio-Cortez of New York. Cisneros is arguing Cuellar is too moderate for the 28th District, calling him President Donald "Trump's favorite Democrat." Cuellar is denouncing the challenge as meddling by out-of-state partisans who do not truly understand the district.

Speaking hours after Bustos at the festival, Pelosi was unequivocal in her support for Cuellar, who was in the audience.

"Absolutely, absolutely, absolutely, absolutely," she said, drawing scattered boos. "I'm very, very proud of Henry's work in the Congress and I'm proud to support him — even if I didn't have a policy of endorsing incumbents."

Asked about the comments by Bustos and Pelosi, Cisneros said in a statement that her campaign "is the only one in this race with an ear to the ground in Texas' 28th Congressional District."

"I’m focused on ensuring that the real concerns of our community are represented in Congress — people like the truck drivers and supply managers who told me yesterday they had no idea NAFTA was being renegotiated and that no one had approached them to hear their concerns," Cisneros said. "We know we are the people's campaign, and we’re confident we will win in March."

Pelosi also talked up Cuellar on the sidelines of the festival, including at a fundraiser for Texas Democrats on Sunday morning in Austin, where she touted his work on immigration and trade. Cuellar attended the fundraiser along with U.S. Rep. Lloyd Doggett, D-Austin, and at one point, Pelosi was listing the different ways in which Texas is diverse and noted it also varied "philosophically — from Doggett to Cuellar." The audience laughed.

Bustos, an Illinois congresswoman, defended Cuellar a second time later Saturday during a panel discussion with Tom Emmer, the chairman of the National Republican Congressional Committee. After the Republican congressman from Minnesota labeled Cuellar the most vulnerable House Democrat in Texas — seeking to emphasize the party's internal rifts — Bustos reiterated that she thought Cuellar would be "fine," crediting him with being "very bipartisan," among other things.

Still, Cisneros' campaign is gaining some traction. She got her biggest boost yet in early September when Democratic presidential candidate Elizabeth Warren backed her and appeared with her at a rally in Austin.

Bustos told reporters Saturday that Warren, the Massachusetts U.S. senator, texted Bustos to give her advance notice that she would be endorsing Cisneros.

"I said, 'Thanks for the heads-up,'" Bustos said. "She told me the day before, so I don't think I was gonna change her mind."