OTTUMWA, Iowa — Bernie Sanders is sending organizers to convenience stores across Iowa and staking out drug stores and even nursing homes.

Pete Buttigieg has a more technocratic model. He’s compiling detailed lists of the personal networks of his supporters, turning them into crowds and sifting through the hundreds of email addresses and cell numbers in hopes of landing them on caucus night Feb. 3.

The approaches are as different as the two men themselves, but represent one of the most important tactical pieces of a presidential campaign in Iowa: getting people to attend the caucuses for the first time.

In the highly competitive Democratic presidential race, expanding the electorate is vitally important for the pack of four candidates straining to break out in the coming two weeks.

And with good reason. The candidate who turns out the most and the broadest array of first time participants stands a very good chance of winning.

“They’ve got to be working new people. There’s nor rhyme nor reason not to,” said Paul Tewes, who directed Barack Obama’s surprise victory in Iowa in 2008. “I pity the ones that aren’t, if that’s the case.”

Certainly, other campaigns are trying to expand the pool of voters, but it is Sanders and Buttigieg who are betting most heavily on attracting the most newcomers.

“A significant part of our strategy is engaging people who have been left out of politics,” said Misty Rebik, Sanders’ Iowa state campaign director. “And we’re doing that by meeting people where they are.”

Sanders’ volunteers set up a table outside a CVS in Cedar Rapids last week, and they talked to people as they entered the store. Others volunteers have become regulars at the familiar red-roofed Casey’s Convenience Stores throughout Iowa, a common daily coffee stop for older Iowans who gather to talk politics. Some campaign volunteers have even recruited some of the Casey’s regulars to help make phone calls from the tables near the pizza counter.

One Sanders organizer was kicked out of a half-dozen nursing homes, which typically are used as satellite caucus locations, after showing up to talk to residents, Rebik said. “But she came back with lots of commit-to-caucus cards,” Rebik said. “That’s all I’m saying.”

When calls to past caucus participants showed signs of being ineffective, the Sanders campaign sent volunteers, wearing “Bernie” T-shirts and carrying clipboards, to approach patrons at farmers markets and parades.

It’s not that Sanders, who narrowly lost the caucus in 2016 to Hillary Clinton, is unfamiliar with traditional organizing, the act of reaching out to past caucus participants by using the Iowa Democratic Party’s voter list.

It’s that Sanders, who this time has multiple top-tier opponents dividing up traditional caucus voters, cannot rely solely on his past supporters, some of whom have decided to back a different candidate in 2020.

Plus, his arm’s-length association with the national Democratic Party, as a self-identified Democratic socialist, has soured relations with many in the party’s establishment, forcing him to look outside the traditional base for support.

Though Chloe Sokolov always considered herself a Bernie supporter, the 25-year-old bartender at Eatery A, a popular Des Moines restaurant, plans to caucus for the first time this year in part because Sanders’ campaign convened more than 50 service industry workers to discuss their economic challenges.

“It was actually a really big turnout, maybe 60,” Sokolov said of the mid-December meeting. “I’ve never caucused in Iowa, but it’s important to me especially this year.”

It’s a part of the numbers game that goes to the heart of the caucus competition.

The best example came in the 2008 Democratic caucuses, when an estimated 58 percent of those who turned out were first-timers. There were a record 238,000 participants, setting Obama, who drew a plurality of them into the process, on the road to the Democratic nomination and the presidency.

It was a harsh lesson for Clinton, who played down the reliability of first-time caucus participants, and finished third in Iowa, despite meeting the targets she set for winning supporters.