Bernie Sanders may endorse a candidate in the Seattle mayor's race. We can't confirm who, but Sander’s group Our Revolution tells KUOW that it's taking a look at Seattle. That kind of endorsement could be huge. With incumbent Ed Murray dropping out and more than a dozen candidates vying to replace him, endorsements may matter more than ever this year. Former King County Executive Ron Sims calls an endorsement "an affirmation by other people that you're respected because you can keep your word and get the job done." Sims' endorsement is itself sought after in this city, and this year he’s backing former U.S. Attorney Jenny Durkan for mayor.

But Sims knows there are many more endorsements to come, including backing by labor, which can be seen as “a big stamp of approval.” Before he dropped out, incumbent Mayor Ed Murray racked up endorsements from around 20 unions. Now many of those endorsements are up for grabs. So how does a candidate earn labor's backing? Sims said based on his experience it's a combination of things. The biggest questions are: What are your priorities and can you get the job done? "People think getting labor endorsements is easy," Sims said. “Oh, no. Every labor union has its issues. Are you going to build? Are you going to be good on transportation issues? Are you going to respect the right for people to organize your labor force?” With so many different unions and people to woo, the endorsement contest is a lot of work for candidates. And in many cases the voters haven't even heard of the individuals or groups that are doing the endorsing. So why do candidates bother?

In the case of labor unions, even as membership numbers decline, their endorsements can help with fundraising. And labor helps turn out the vote. David Rolf, head of SEIU 775, said labor's backing in this city still matters a lot. Rolf stood behind Murray as the mayor announced he would not be running. "Within the city of Seattle, probably 25 percent of the workforce belongs to a union," Rolf said. "Seattle's a very strong union town with a very strong working-class history, and probably five out of the last six mayors got elected with substantial union support." Whether it’s from Bernie Sanders or a local union, an endorsement can matter in a crowded field, said Margaret O'Mara, a history professor at the University of Washington who writes about American politics. Also factored in is low name recognition for some candidates. "When you have these third-party validators attesting to someone's qualifications for mayor, that can be a guide," O'Mara said.

But O'Mara also said the power of endorsement can be diluted when there are lot of candidates. "Where endorsements will be interesting is whether you have all of the people and organizations endorsements that lined up behind Ed Murray all going en masse to one candidate," she said, "or if they will get spread out across a number of candidates." There are more than a dozen candidates in the Seattle mayor's race. The list includes: Former U.S. Attorney Jenny Durkan

State Representative Jessyn Farrell

State Senator Bob Hasegawa

Former Mayor Mike McGinn

Urban planner Cary Moon

Attorney and community activist Nikkita Oliver One person who won't be on the list: City Councilmember Lorena Gonzalez, who had been widely mentioned as a possible candidate. She said Tuesday that she'll seek re-election to her council seat, not the mayor's office.