Walker, 31, became the first black member of Linn County’s Board of Supervisors when he was elected in 2016. Linn, whose seat is Cedar Rapids, is the second-most populated county in the state.

Walker’s nod comes on the heels of Sanders winning the endorsements of Reps. Alexandria Ocasio-Cortez and Ilhan Omar. Sanders’ aides hope Walker and the members of the so-called “Squad” will demonstrate that a “multigenerational, multiracial working-class movement” is behind him.

Walker is expected to officially announce his endorsement at a rally with Sanders in Iowa City on Friday. According to excerpts from his prepared speech, he will argue that Sanders is the best candidate because he has a bold vision, diverse base and longtime progressive record.

“Whether it was standing up for the rights of the LGBTQ community in the 1970s or calling out the harm of money in politics throughout much of the last decade, his voice has been a consistent one,” he states in his planned remarks. “This is why I trust him to do the right thing when the political winds are blowing hard against the sails.”

Walker, like Sanders, has anti-establishment bona fides: After deciding against a run for the U.S. Senate next year, Walker decried the primary as a race “orchestrated by Washington elites, instead of being left up to the voters.” Senate Minority Leader Chuck Schumer is backing Theresa Greenfield in that election. Walker has backed another candidate, Kimberly Graham, who supports single-payer health care.

The Sanders team is also expected to name Walker as its first Iowa campaign co-chair.