Insurgent Democratic presidential candidate Bernie Sanders will officially pick up his first congressional endorsement Friday at a rally in Tucson, Arizona, from the area’s congressman, Rep. Raul Grijalva, who is also the co-chairman of the Congressional Progressive Caucus.

Sanders has the support of one of four Democratic voters nationally, but – until now – zero out of 232 Democratic members of Congress. Democratic front-runner Hillary Clinton’s lock on the party’s leaders has left little room for endorsements for Sanders or Vice President Joe Biden, should he decide to jump in the race.

Political scientists say endorsements from party elite are the most determinate of success in party primaries, but Sanders has run an intentionally outsider campaign and his campaign believes endorsements are less important than pundits think.

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In an interview with MSNBC Wednesday, Grijalva, whose endorsement was first reported by The Los Angeles Times, said he wanted to make his support for Sanders public before the first Democratic debate next week.

“I support Bernie’s message. I think it’s an important message. It’s a message that has unfortunately been muted for too long,” Grijalva said.

The congressman said he did not realize he was the first member of Congress to back Sanders, but added he hopes others will give Sanders the consideration he deserves. He does not, however, plan to lobby his colleagues to endorse Sanders.

“For some of my colleagues it’s been a rough process about deciding whom to endorse,” he said. “I’m not going to go out and solicit, it’s a personal decision … If people ask me why and want to discuss this with me, I’ll be more than glad to discuss it.”

Grijalva, whose district is heavily Latino, thinks Sanders can expand his support among Hispanic voters and wants to help the Democratic presidential candidate do that. “One of the accusations is that Bernie has no reach into communities of color. I think people are mistaken about that,” Grijalva explained.

Grijalva added that his endorsement is not meant as a sleight against Clinton, whom he respects and whose campaign courted him as well.