Socialist presidential candidate Sen. Bernie Sanders (I., Vt.) continued his clash with establishment Democrats Wednesday, as he endorsed a progressive attempting to unseat an incumbent House Democrat backed by party leadership.

Sanders announced his support for progressive Jessica Cisneros in her primary fight against Rep. Henry Cuellar (D., Texas), saying the incumbent Democrat does not "understand that real change comes from the bottom on up, not the top on down." Cisneros backs the same far-left policies associated with Sanders, including Medicare for All, the Green New Deal, and a $15 minimum wage.

The endorsement comes as Democratic leaders scramble to stop Sanders's rise in the party's presidential primary just days before the Iowa caucuses, fearing the Vermont senator's socialism could bolster President Donald Trump's reelection bid and hurt Democrats in swing districts. National party leaders have stood by Cuellar despite Cisneros's attack that he is "Trump's favorite Democrat." House Speaker Nancy Pelosi (D., Calif.) and Democratic Congressional Campaign Committee (DCCC) chairwoman Cheri Bustos endorsed Cuellar.

Cuellar's campaign pushed back against Sanders's endorsement, arguing the Vermont senator's out-of-state influence will fail to woo Texas voters.

"While our opponent continues to focus on out-of-state celebrity endorsements, we are focused entirely on support from people who actually live and work in this district," Cuellar spokesman Colin Strother told the Washington Free Beacon. "That's why we have endorsements from over 225 local elected officials and she has zero. When it comes down to being organized on the ground and mobilizing voters, we think those strategic partnerships will add significantly more value."

The Cisneros campaign did not respond to a request for comment.

Cisneros is backed by Justice Democrats, the progressive group that supported Reps. Alexandria Ocasio-Cortez (D., N.Y.) and Ilhan Omar (D., Minn.) in 2018. She has racked up numerous national endorsements since launching her campaign in June, touting support from Ocasio-Cortez, Sen. Elizabeth Warren (D., Mass.), NARAL Pro-Choice America, and the Planned Parenthood Action Fund, in addition to Sanders.

Cuellar has criticized Justice Democrats' role in the primary, saying that "it's a radical, far-left group that wants to impose [its] vision from New York into South Texas." A previous Free Beacon analysis found that Cisneros received just 1.8 percent in campaign contributions from inside the district she hopes to represent.

As Sanders surges in early primary states—he holds a nine-point lead in Iowa according to an Emerson College poll released Tuesday—establishment Democrats have expressed concern that the Vermont senator is too radical to win over American voters. Sen. Amy Klobuchar (D., Minn.) argued Sunday that she would "make our tent bigger" than Sanders because she does not "come from a state as blue as Vermont." Former South Bend, Ind., mayor Pete Buttigieg warned against Sanders's electability in a Saturday fundraising email. Former vice president Joe Biden has called himself "the best candidate to beat Trump," while criticizing progressive candidates for being out-of-step with the average American.

Sanders's 2020 rivals appear tame when compared with the party's 2016 nominee, former secretary of state Hillary Clinton. In her campaign memoir, What Happened, she accused Sanders of entering the primary race to "disrupt the Democratic Party." Clinton doubled down in January, calling Sanders a "career politician" that "nobody likes."

"He was in Congress for years. He had one senator support him," Clinton told the Hollywood Reporter. "Nobody likes him, nobody wants to work with him, he got nothing done. He was a career politician. It's all just baloney and I feel so bad that people got sucked into it."

The Sanders campaign did not respond to a request for comment.