Nan Horvath stood on a front lawn Sunday in her hometown of Johnston clutching a Martin O’Malley yard sign. The day was unseasonably warm for Iowa for the last day of January, about 40 degrees, and Horvath wore a thick cream cable knit sweater with no overcoat. She watched, almost wistfully, as her longshot candidate delivered one of his last speeches in Iowa—and maybe one of his last of his presidential campaign.

O’Malley was polling at just 3% in the last Des Moines Register poll before Monday’s caucuses and has little chance of winning the state or the nomination. But that 3% could prove pivotal—not to O’Malley but to his rivals, Hillary Clinton and Bernie Sanders. That Register poll found Clinton slight ahead of Sanders 45% to 42%, within the survey’s 4 point margin of error.

Why would O’Malley’s supporters mean anything to Clinton and Sanders? Because the Iowa Democratic caucuses have a 15% viability threshold. Any candidate who doesn’t receive 15% of support in the first round of voting in each of the 1,682 caucuses is eliminated and those supporters must choose between the remaining candidates on the ballot in the second round. Depending on how they break, O’Malley’s 3% could mean the difference between a win or loss for either Clinton or Sanders.

Read More: Here’s Everything You Need To Know About the Iowa Caucuses

O’Malley, of course, bristles at the suggestion. “My message to you when you go into caucus is to hold strong,” he bellowed across the lawn in Johnston, “Fight for viability and fight for the country!”

But Horvath, 59, is realistic. She admits O’Malley likely won’t be viable in her caucus and she already has a second choice picked out: Hillary Clinton. Clinton folks courted her heavily, sending three separate teams to knock on her door and ask for her second round support face-to-face. The Clinton campaign has been spending a lot of time contacting voters like Horvath. On Saturday surrogates Bill DeBlasio, the mayor of New York, and former Iowa Gov. Tom Vilsack spent all day calling O’Malley supporters.

The Clinton campaign motto this time around is fighting for every vote. And their extensive ground game bears that out. Barack Obama won Iowa in 2008 with two main ingredients, a soaring, inspirational message of hope and change, and a community organizer’s background which he people applied to great success at the Iowa caucuses. Clinton and Sanders are splitting Obama’s talents in 2016. Sanders is betting that his brand of political revolution will inspire thousands of new and drop off voters to caucus, while Clinton has meticulously organized Iowa from the bottom up. Monday night, America will see which branch of Obama’s legacy will win the next generation.

In courting O’Malley supporters, the Clinton campaign is taking a page from Obama’s campaign which invested heavily in convincing voters dedicated to third tier candidates, such as Sens. Chris Dodd and Joe Biden, to pick Obama as their second choice. And that’s not the only Obama organizing tactic they are deploying. In some cases, the Clinton team might try to boost O’Malley’s ranks to harm Sanders.

Read More: There’s a Tourist Epidemic at the Iowa Caucuses

The Clinton team has trained caucus chairs to shift some supporters to O’Malley if the conditions are advantageous in order to deprive Sanders of an extra delegate. Precinct campaigns are using a custom campaign app that does the caucus math for the volunteers. News of the app was first reported Saturday by BuzzFeed News, but precinct leaders have been trained for weeks in the tactic, according to Clinton campaign officials.

The head-spinning approach of ceding support to a lesser-performing rival in order to minimize a better-performing one’s delegate count is hardly novel, having been used in 2004 by the Kerry campaign and by both Clinton and Obama against each other in 2008.

The strategy works by allowing the poorer-performing candidate, in this case O’Malley, to meet the viability threshold—the level of support at which he can be awarded a single delegate. In most caucus locations that’s 15% of attendees, but rises to 25% in precincts that award just two delegates. Unlike the Republican caucuses who use a secret ballot, Democrats vote with their feet, physically moving to different corners of the room. If a candidate’s support is below the viability threshold, the caucus chair will inform his or her supporters that they have to choose between the remaining candidates. That is, unless supporters from one of the other groups moves over to bolster their numbers.

Clinton’s Iowa campaign manager Michael Halle worked for both Obama campaigns in Iowa. On Monday, the army of volunteers he has marshaled—numbering in the thousands—will deploy from 150 staging locations around the state that are completely volunteer-run along with the 26 organizing offices. They will babysit kids and drive buses to pick up the elderly from nursing homes. They will place Hillary signs and stickers at caucus points and, perhaps most importantly, help the 4,200 trained precinct captains with everything they need to sway their neighbors come caucus time such as literature on Clinton’s positions.

All that organization on the ground has given Clinton her slight advantage in the polls. Amongst voters who’ve caucused before, Clinton’s lead expands. And 83% of her caucus goers have made up their minds versus only 69% of Sanders’, according to the Register poll.

Sanders also has a massive organization with 15,000 volunteers. But he has fewer trained precinct captains. Sanders supporters tend to have far less interest in other candidate supporters, and it is unclear how many Sanders caucus-goers are waiting in Martin O’Malley’s ranks. A spokesperson for Sanders campaign did not respond to repeated requests for comment on volunteering figures.

Ultimately, the caucuses are likely to be decided by turn out. Sanders is betting his campaign on bringing new voters into the system such as millenials, promising them a political revolution. As Sanders himself said on Saturday, “If you show up to caucus, if turn out is large, we will win. If you don’t, we will lose.” A smaller turnout of regular caucus-goers, say 140,000 people, means a win for Clinton.

While Sanders is betting on new folks showing up, Clinton’s strategy is focused on proven voters, thus the O’Malley push. Those are voters they know will already be in the room. “Hillary’s people really worked for my vote,” Horvath says. “I really wish Gov. O’Malley had caught on. But I won’t be unhappy to vote for Hillary if it comes to that.”

Additional reporting by Sam Frizell and Zeke J. Miller

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