Progressive Democrat Jessica Cisneros of south Texas notched another key endorsement on Wednesday as Sen. Bernie Sanders announced his support for the human rights attorney's primary election bid to unseat Rep. Henry Cuellar.

Laredo-born Cisneros is seeking to defeat Cuellar in Texas's 28th district. Cisneros has dubbed Cuellar, a 15-year incumbent, "Trump's favorite Democrat."

In a statement cheering the new endorsement, Cisneros tied her run to Sanders's 2020 presidential campaign.

"I'm so grateful to receive the endorsement of Senator Bernie Sanders who is running a grassroots campaign to fight for working people, not big corporate donors," said Cisneros. "We're proud that presidential candidates are taking a close look at South Texas as we fight to turn Texas blue in November—and that they know we're the only candidate in this race who will champion Democratic values in Washington."

I'm so grateful to receive the endorsement of @BernieSanders, who's running a grassroots campaign to fight for working people, not big corporate donors. https://t.co/MqxPro6DfM — Jessica Cisneros (@JCisnerosTX) January 29, 2020

Sanders, in a statement Wednesday, welcomed the fact that Cisneros was just one of a number of 2020 candidates who could usher in progressive policies.

"This is the most important election in our lifetime and I’m proud there are so many candidates running for Congress who understand that real change comes from the bottom on up, not the top on down," said Sanders, who's also backed Rep. Alexandria Ocasio-Cortez (D-N.Y.) and Marie Newman of Illinois. "They're all strong advocates for real change and together we will build a movement to transform this nation so that it works for all our people."

Cisneros is backed by Justice Democrats, the political action committee that helped Ocasio-Cortez in her successful challenge to 10-term Congressman Joe Crowley. Cisneros getting Sanders's endorsement, said Justice Democrats, is "huge."

"Jessica is building a movement in South Texas that is standing up to the most powerful forces in our country," said Alexandra Rojas, executive director of Justice Democrats. "We're proud she's received this endorsement from Bernie who has dedicated his career to fighting for working families and needs fighters like Jessica in Congress to enact a bold agenda."

Huge! @JCisnerosTX is taking on the most powerful corporations and special interests in her bid to unseat Trump's favorite Democrat: Henry Cuellar.



We're so proud of this endorsement from @BernieSanders who has dedicated his career to fighting for working families. pic.twitter.com/IhPTc0f40R — Justice Democrats (@justicedems) January 29, 2020

The Sanders announcement comes a day after the Cisneros campaign announced endorsements from three progressive groups—Sierra Club, Texas Organizing Project (TOP), and Stonewall Democrats of San Antonio. Those organizations join a growing list of voices supporting her challenge to Cueller, such as the AFL-CIO, EMILY's List, National Nurses United, and NARAL Pro-Choice America, as well as Democratic presidential primary candidate Sen. Elizabeth Warren. Despite the increasing support, Cisnernos says Cuellar continues to refuse to debate her.

"When we are judged in the future, it will be by our actions at this moment," Cisneros said Tuesday, "how we stood up for our working families, how we advocated for our most vulnerable populations, and how we fought for our planet."