In late December, Joe Biden was still leading the pack of Democratic Party presidential hopefuls in California as they campaigned for the state’s huge trove of delegates in the March 3 Super Tuesday vote. Yet there was something a little lackluster about his presence in the state: He hadn’t made many visits in recent months, and had only one fully staffed office in California and barely 20 paid staffers.

Biden’s low-key presence in the state was particularly surprising given how much he needed a big showing here. He had or would soon secure the endorsement of a host of big names in California politics, from LA Mayor Eric Garcetti to Sacramento Mayor Darrell Steinberg, to Senator Dianne Feinstein. But as the first caucuses and primaries neared, Biden’s campaign here seemed stuck in low gear.

Close behind him in those December polls was Bernie Sanders, with Elizabeth Warren not too far off in third place. Since October, however, the three candidates’ fortunes had gone in different directions. Biden and Warren were seeing their support levels dip in the Golden State. Sanders, by contrast, was getting stronger by the week.

On December 21, the Vermont senator came to Southern California to hold a rally in Venice Beach. At that rally, he endorsed Peoples Action’s “Homes Guarantee” plan, which the progressive organizing group Ground Game LA helped produce. The plan is an ambitious package of policy proposals designed to translate the aspiration of providing homes to the state’s growing homeless population into reality. It is, says organizer Bill Przylucki, “a spectrum of policy recommendations that we will start guaranteeing housing as a human right. We want to make it the Medicare for All for housing.”

Elizabeth Warren and Julián Castro had also incorporated aspects of the Homes Guarantee plan into their policy platforms, but only Sanders wholeheartedly embraced the specifics of it, signing on to a Home Guarantee Pledge that the grassroots group was asking candidates for local, state, and national office to take. At that Venice Beach rally, Ground Game LA, which works to organize poor communities and non-English-speaking people in the huge metropolitan area, returned Sanders’s favor and endorsed his candidacy.

Around the state, a similar dynamic was unfolding. While some of the candidates were struggling to field staff for even a handful of offices, Sanders, by year’s end, had more than 20 offices and over 100 full-time paid staffers dotted around California. Those offices also had thousands of volunteers putting in time to canvass, phone bank, and so on. Over the past year, explains Anna Bahr, the LA-based communications director for the campaign, Sanders’s team had worked to establish a long-term presence not only in the big coastal cities but in small towns and communities in the Central Valley, the Inland Empire, and other poorer, less media-visible parts of the state.

It was smart politics. Early on, the campaign had realized the vital importance of taking advantage of California’s having moved its primary from June—a date that had rendered it largely irrelevant in the selection of candidates during past primary seasons—to early March, and of reaping a delegate payoff from the country’s largest, and arguably most progressive, state at a vital moment in the campaign. “We have been knocking on doors that have never been knocked on before,” says Bahr. “Meeting people where they are and in the language they speak. We have been holding press conferences in Cantonese and so on.”

By year’s end, it was clear that Sanders’s grass roots presence in the state was paying off. Polling showed that he and Biden were now vying for front-runner status. By late January, as Biden’s support began to crater, and as Warren’s candidacy began to sputter after a strong autumn, one poll after another showed Sanders carving out a significant lead. Today, those same polls show Sanders with roughly double the support of Biden. If the Vermont senator maintains that lead over the next week and if his rivals split the vote and mostly fail to reach 15 percent of the statewide vote, he will likely come away with a large majority of California’s more than 400 delegates.

But while Sanders is clearly ahead, the other Democratic candidates are also hoping to use California, and its huge trove of delegates, to catapult their campaigns forward.

Warren in particular has, like Sanders, spent more than a year building up huge on-the-ground networks in all corners of the Golden State, repeatedly holding rallies and mobilizing organizers not just in LA and San Francisco and the other hubs, but throughout the Central Valley, in poor desert communities, and in northern mountain towns. Yet, in most recent polls, she has failed to break out from the pack that is chasing Sanders.

Others, like Klobuchar and Buttigieg, perhaps unsure until recently whether they’d still be in contention this late in the process, have only recently got their efforts up to speed here and are operating on a much smaller canvas. Klobuchar’s poll numbers are in the low single digits in California; Buttigieg, who hired as his state director Cecilia Cabello, who directed Hillary Clinton’s California campaign four years ago, is doing significantly better.

The strategy of team Buttigieg is simple: They hope that a sophisticated district-by-district effort will allow him to reach the 15 percent threshold and thus win a significant number of delegates, an outcome that will, they believe, allow his campaign to continue the fight even if Buttigieg loses heavily in the popular vote totals. (Most of California’s delegates are determined by the percentage of the vote each candidate gets statewide; but more than 270 additional delegates are parceled out on a district-by-district basis to candidates who cross the 15 percent threshold locally.) “It’s all about winning delegates,” says Buttigieg campaign spokesman Ben Halle. “The way to do that is reaching viability in as many of the 53 congressional districts as you can.”

Buttigieg was recently endorsed by the state’s lieutenant governor, Eleni Kounalakis, and has made a late effort to woo voters by holding a series of town hall meetings in LA and in the state capital of Sacramento.

And then there’s Mike Bloomberg, who bypassed the early primaries and caucus contests, joined the contest late, and whose entire strategy rests on vast advertising expenditures—thought to be vital in a state as large and diverse as California—and a bank account that has allowed him to make up for lost time by opening 23 offices and hire upward of 800 staffers, which his campaign touts as “the largest California ground game in presidential primary history.” In the past couple of weeks, the Bloomberg campaign has hosted a huge number of events, ranging from a Surfers for Mike rally in Southern California to a Climate Scientists for Mike rally up north. They have sought to draw a contrast between Bloomberg and Sanders on the issue of support for gun control, in a state where voters strongly favor a range of such measures. And they have touted Bloomberg’s long-standing support for policies aimed at tackling the crisis of climate change.

Bloomberg hoped that his media blitz in California would generate a result that would knock out the other moderate candidates and leave the field clear for him to present himself as the middle-ground alternative to Trump on the right and Sanders on the left. The campaign, says state communications director Michael Buckley, is pitching itself to “Democrats who are center, more moderate. To independents, to left-leaning or moderate Republicans. We do very well with suburban women.”

So far, however, the polling doesn’t indicate that the strategy has worked. Instead, it looks more like Bloomberg is further dividing the moderate wing of the party, thus making it easier for Sanders to rack up a hefty victory in California.

The Ground Game LA organizers are growing more confident that Sanders will emerge from the California primary as the clear favorite to win the Democratic nomination. “For people who’ve been working in community organizing for a long time,” says Ground Game’s Kendall Mayhew, “we have a candidate listening to our strategies and what we have been doing, investing in voters with a long-term strategy, not just helicoptering in at election time. The ground game the Sanders campaign has built here is enormous—and the people they have hired are people in those communities, which is incredibly important.”