Katie Orr  | KQED

About 2.5 million union members call California home. With election season upon us, the two Democrats fighting for their party’s presidential nomination see union support as critical to getting out the vote.

Former Secretary of State Hillary Clinton gave unions a shoutout at a recent rally in Oakland.

“We need strong unions, and I will stand up for that basic American right,” she told a cheering crowd.

Clinton has been doing well with labor, collecting major endorsements from unions representing teachers, government employees and food workers. Clinton also has the support of the Service Employees International Union.

Yvonne Walker is president of SEIU Local 1000. She says it’s not just that Clinton is better on one issue or another. Rather, she says, it’s their long history of working together on issues that tilted their endorsement toward Clinton instead of Vermont Sen. Bernie Sanders.

“She is part of all of our platform, be it women and children, economics, all of that in a very real way,” Walker says.

But Sanders has his labor supporters, too. He has endorsements from communication workers, health care employees and postal workers.

Among his most visible backers are the California Nurses Association and its umbrella organization, National Nurses United. The groups are powerful allies for Sanders. Records show the national organization has spent nearly $4 million on behalf of the Sanders campaign.

The nurses recently rallied for Sanders at the state Capitol.

Deborah Burger, co-president of both unions, said Sanders is the only candidate who would represent everyone in the United States. She jokes that he essentially stole their platform.

“We’ve been working on single-payer Medicare for all. We’ve been working on securing Social Security and expanding it,” she says. “And we’ve been trying to make sure that people can go to college and not end up with a mountain load of debt.”

Burger says her organization is sticking with Sanders until the end and will make sure that he has a major influence on the platform that Democrats adopt at their convention in Philadelphia.

Such steadfast support is crucial to candidates. Kent Wong directs the UCLA Labor Center. He says even though union membership is declining, organized labor is still a powerful political player.

“Labor’s endorsement has had a huge impact in opening up financial resources as well as campaign activists,” he says. “So when a candidate receives a labor endorsement, it’s a big deal.”

Though the ongoing nomination fight between Sanders and Clinton has been tough, Wong says he expects labor to come together for the general election. In fact, he expects union members to be even more energetic since Donald Trump is the presumptive Republican nominee.

“He is fiercely opposed to unions, to worker rights,” Wong says. “And so I do think that this will be a strong rallying cry for unions and workers across the country who want to oppose Donald Trump and the policies that he represents.”

Copyright KQED 2016. Read more in this series and let us know your thoughts on Twitter using the hashtag #CACounts.