Democratic presidential hopeful Bernie Sanders’ latest campaign stop in Michigan scored a set of endorsements from influential progressive leaders, boosting his credentials while Sanders competes with Elizabeth Warren to lead the progressive movement.

The two Senators are running on similar campaign themes, putting them on a collision course while primary voters consider who is best equipped to champion Medicare for All and other dramatic reforms to address corruption and inequality. National polls found Sanders, I-Vt., and Warren, D-Mass., were deadlocked in second place behind former Vice President Joe Biden, but Warren began to pull ahead in September.

Sanders was losing ground when a heart attack forced him to suspend campaigning for two weeks in October. The Vermont Senator bounced back and participated in the next primary debate in Ohio, then held a large rally in New York and picked up endorsements from U.S. Reps. Rashida Tlaib, D-Detroit; Alexandria Ocasio-Cortez, D-N.Y.; and Ilhan Omar, D-Minn.

A thumbs up from other politicians isn’t enough to secure the Democratic nomination, said David Dulio, director director of Oakland University’s Center for Civic Engagement. However, endorsements are important in Warren and Sanders’ competition to show who will be the best progressive alternative to Biden.

“I think those particular endorsements could be particularly important because you’ve got Warren and Sanders fighting for the same votes,” Dulio said. “I think we’re going to end up with an establishment lane and a progressive lane. At the end of the day, there’s only going to be room for one in each of those lanes.”

The endorsements show progressive leaders believe Sanders is "the only candidate running who has the guts to take on the corporate elites and the billionaire class,” Sanders Campaign Manager Faiz Shakir said in a statement.

Warren also took a tour of Tlaib’s district this year, visiting Detroit neighborhoods affected by industrial pollution. Warren endorsed Tlaib in 2018, while Tlaib praised Warren several times on social media throughout the primary.

Mike McCollum, Michigan state director for Warren’s campaign, declined to comment on the value of endorsements from leading progressive figures.

“We’re laying the groundwork in Michigan and all across the country to build a movement of grassroots supporters that will own a piece of this campaign and be in the fight with us," McCollum said in a statement. "From standing with GM workers on the picket line to meeting with mothers in the most polluted zip code in the state, Elizabeth Warren is working to earn as many votes as possible when the people of Michigan make their voices heard on March 10th.”

One key difference between Sanders and Warren is the age of their supporters, said EPIC-MRA pollster Bernie Porn. Sanders is the oldest Democrat in the primary but is most popular among 18-29-year-old voters -- Warren’s supporters have a more even age distribution but trends older.

Tlaib and the other progressive congresswomen are the young faces of a political revolution they said Sanders started with his 2016 presidential campaign. Tlaib endorsed “uncle” Sanders at a Sunday rally in Detroit after inviting him on a tour of her congressional district.

Tlaib told an energized crowd in Detroit that voters “deserve someone who writes the damn bill.” Sanders has used the phrase at primary debates to demonstrate his unique authority on Medicare for All, a policy Warren also adopted as part of her healthcare agenda.

“There’s something so incredibly inspiring about someone that we know is not going to sell us out, that’s not going to bow down to these structures that are so built on racism, so built on choosing those that are wealthy,” Tlaib said in a video explaining her endorsement. “He’s consistent in saying he’s with us first. He will always choose us first.”

Mark Grebner, a Democratic strategist who founded Practical Political Consulting in East Lansing, said the endorsements help bolster Sanders’ democratic-socialist image, but probably won’t have much impact on the primary. Warren’s persona offers more moderate appeal, Grebner said, and she wasn’t likely to earn endorsements from “the squad” anyway.

Still, Grebner said Warren has surprisingly few high-profile endorsements from politicians.

Dulio said endorsements from divisive figures like Ocasio-Cortez and Tlaib could hurt Sanders in the general election if he secures the nomination. Sanders was already likely to face attacks for being too “radical” -- that was the message of a counter-rally staged Sunday by Michigan Trump Republicans -- and Dulio said Tlaib would be the star of anti-Sanders ads.

“In a state like Michigan that went for Trump last time, albeit by a small number of votes, that could be a yoke around his neck," Dulio said.

Endorsements from a diverse group of Democrats could also help Sanders perform better with minority communities in Wayne County. Sanders fell 22 points behind there in the 2016 Democratic primary, despite winning Michigan by a narrow margin.

Biden leads the field in support among African Americans, according to Morning Consult polling, a key reason he remains the front-runner according to Porn. Sanders leads with black voters ages 18 to 29, but falls far behind Biden in other age groups.

Sanders and Warren have largely been cordial and avoided attacking each other during debates. National polling suggests supporters for Warren and Sanders would be likely to support the other candidate if their first pick fails to secure the Democratic nomination.

Warren’s surge indicates she is picking up some of Sanders’ supporters, Porn said.

“If Bernie were to continue to slide or if he were to end up getting out of the race all of a sudden, I think Warren would pick up a lot of support from Bernie and probably be catapulted into a stronger position to be the nominee,” Porn said.

The Working Families Party, a labor-aligned progressive group, endorsed Warren after supporting Sanders in 2016. National Director Maurice Mitchell said Warren “strikes fear into the hearts of the robber barons who rigged the system," and acknowledged Sanders and Warren shaped the “ideological terrain” on which the primary is being waged.

U.S. Rep. Andy Levin, D-Bloomfield Township, endorsed Warren in July after embracing Sanders’ Medicare for All plan during his 2018 congressional campaign. Levin, a member of the Congressional Progressive Caucus, said at the time that Warren is the best candidate to beat President Donald Trump and “lead a transformative government."

Former supporters are considering Warren in part due to Sanders’ recent health issues, Grebner said, which “crystalize” concerns about his age and endurance.

“Bernie’s just not gonna win the chess game,” Grebner said. “Warren may. I think Biden may. Buttigieg may ... I mean, even if one of the horses ahead of (Sanders) falls, it doesn’t matter because he’s slower than the other horses ahead of him. You’re a half mile for the finish line and Bernie is wheezing.”

Dulio said it’s too early to count Sanders out.

“I think that thought was more when he was off the trail, recovering from his health scare, but he’s come back and there’s really been little or no mention of it,” Dulio said. “He’s getting these endorsements from these from these key players in the progressive wing of the party, and I don’t think I don’t think you can write him off at all.”

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