The caucuses that kick off the 2016 presidential election season were 104 days away. But on the second floor of a tired, rusting office building next to a mini-mart here, a dozen or so people were hard at work trying to elect Hillary Rodham Clinton.

Eileen Williams-Jackson, 52, was dialing uncommitted Iowa Democrats. How do you feel about Hillary? Did you watch last week’s debate? Can we meet to talk about caucusing for her?

Norm Bauer, 62, penned personalized letters to his neighbors — by hand and in cursive — about why he’s supporting Clinton. “It gets numbing,” he said. “Your hands are sore, and your elbows are sore. But I will stick with it. I really want her to be president.”

Similar scenes played out this month in Clinton field offices across Iowa, which now total 20. Clinton is building a campaign juggernaut on a scale beyond that of any other Democratic or Republican campaign, harnessing the data analytics reshaping modern politics and appropriating the personalized organizing techniques Barack Obama used to defeat her in the 2008 Iowa caucuses.

Clinton’s organizing is a course correction from 2008, when she was out-hustled by Obama precinct by precinct. For her Iowa staff of at least 78 and volunteer corps of hundreds, one of the first big tests came Saturday at the Iowa Democratic Party’s Jefferson-Jackson Dinner, which draws thousands of activists and traditionally has been a pre-caucus proving ground.

Clinton is banking on a robust operation to propel her to the nomination and give her a head start in the general election. The strategy is to maximize activity from her supporters and, if needed, manufacture enough enthusiasm to withstand any bursts of momentum for her top challenger, Sen. Bernie Sanders (I-Vt.). What she may lack in passion Clinton hopes to make up for with hard work and tactics.

“Organizing creates a durable, engaged group of supporters that aren’t going to be flighty,” said Michael Halle, Clinton’s Iowa caucus director. “. . . When you have a personal tie to something, you’re not going to be moving around because of a bad news story or a bad Des Moines Register poll. You are dialed in and focused, and that support base is designed to withstand anything.”

The Clinton team is deliberate about changing its culture from one many Iowa Democrats derided in 2008 as arrogant and entitled. Volunteers said they get thank-you notes in the mail. During her visits to Iowa, Clinton meets privately with the most active volunteers and calls other supporters to check in. At Saturday’s dinner, her campaign rewarded a handful of them by seating them at singer Katy Perry’s table.

Supporters have created localized hives of activity, including recreational groups (“Kayakers for Hillary”), yoga classes (“Yogis for Hillary”) and biweekly student chats at Molly’s Cupcakes near the University of Iowa campus. Monday, volunteers planned 150 house parties to celebrate Clinton’s 68th birthday.

At Clinton’s events, she often is introduced not by big-name surrogates but by the campaign’s local organizers, helping raise their profiles in the communities they cover.

“We want to build relationships with caucus-goers,” said Lauren Brainerd, the regional organizing director who oversees the operation up and down the Mississippi River, including in Davenport. “We don’t like being a part of a large campaign machine, and volunteers don’t like it, so we’ve been very intentional about creating a unique experience.”

‘A strategic imperative’

The Clinton campaign, which has raised $76.5 million, is using its fundraising advantage to spend heavily on its ground game in Iowa and the three other early-voting states — New Hampshire, Nevada and South Carolina. It also is beginning to expand its footprint in states that hold March contests.

Clinton headed into October with a staff of 511, and the campaign’s payroll for July, August and September reached $8.5 million, according to Federal Election Commission filings. The campaign has spent more than $1 million to rent office space in its first six months, the filings show.

Clinton campaign manager Robby Mook called the investments “a strategic imperative.”

“We believed it was important to make an early and significant and real investment in Iowa and the other early states, and then states around the country,” Mook said.

In Iowa alone, the campaign had 78 staffers as of early September; it declined to provide more current numbers. Clinton has been building the Iowa organization from Day One, opening nine field offices within two months of her April launch. This spring, her staff had more than 6,000 one-on-one coffee meetings with key activists. By the first week of June, the campaign had signed up at least one supporter in each of the state’s 1,680 precincts — a difficult feat considering some rural precincts have only a few registered Democrats.

“It’s a pretty big deal that they were able to accomplish that,” said Brad Anderson, who directed Obama’s Iowa campaign in 2012. “I don’t think anyone questions the strength of the Hillary organization. Right now, the big question is who of these new people that are coming out for Bernie Sanders will actually show up on caucus night.”

The Sanders campaign started more modestly but is catching up to Clinton thanks to a surge in fundraising and grass-roots interest. As of last week, Sanders had 17 offices and a staff of 68 in Iowa, said Robert Becker, the campaign’s Iowa state director.

“We’re not as big as they are, but the one thing that we feel pretty confident about is that we’ve got a much more enthusiastic base of support in terms of volunteers,” Becker said. “If the caucuses were held tonight, she wins. But we’re still 104 days out, and we feel very good about the arc we’re on.”

A Des Moines Register-Bloomberg Politics Iowa poll released Thursday showed Clinton leading Sanders 48 percent to 41 percent.

One afternoon last week, Sanders’s office in Davenport was buzzing as volunteers drew posters and called supporters to offer tickets to Friday night’s “#RockTheBern” concert.

Asked how Sanders could defeat the better-organized Clinton, Jerry McConoughey, 77, a retired Army officer, pointed to his fellow volunteers: “This is what’s going to beat her — right here, the grass roots.”

The Republican campaigns are much smaller. Donald Trump and former Florida governor Jeb Bush, who have among the biggest GOP footprints in Iowa, have 13 and 10 staffers, respectively. Retired neurosurgeon Ben Carson and Sen. Marco Rubio (Fla.) have smaller but growing teams.

Sen. Ted Cruz (Tex.) relies heavily on volunteers, and his spokesman, Rick Tyler, would not say how many staffers are in Iowa. “Our model is very different than Clinton,” he said. “Paid staffer to paid staffer, for us, would be a most unfair comparison.”

Republicans also insist they will have plenty of time and money to catch up. Strategist Tim Albrecht, who is advising Bush, said the GOP has “solved the organizing problem” and pointed to the 2014 midterm elections, when Gov. Terry Branstad (R) and now-Sen. Joni Ernst (R) cruised to easy wins in Iowa.

There are also ambitious plans by outside groups — including Americans for Prosperity, funded by the billionaire industrialist Koch brothers — and the Republican National Committee to build a ground game in Iowa and other general-election battlegrounds.

‘Super Bowl of organizing’

The Clinton campaign is busy this fall training precinct captains — people known in their neighborhoods who understand the caucus rules and can not only get people to show up at the appointed time but also give remarks at the caucus that persuade people to Clinton’s side.

“That conversation outweighs almost any kind of media anyone could put out there,” said Halle, who was a field staffer for Obama’s 2008 Iowa campaign.

To rehearse, some Clinton offices are staging “candy caucuses,” asking volunteers to organize on behalf of their favorite Halloween candy.

“It’s the Super Bowl of organizing,” Janice Rottenberg, a regional organizing director, said after meeting with volunteers in the Iowa City office. “Nothing requires more focus and attention than the Iowa caucus. It’s important we do this work the right way. It’s not just knocking on the most doors, but we want to make sure we take the time to have real conversations.”

“Conversations” is a buzzword around this second Clinton campaign. In 2008, her team took a lot for granted. Jean Pardee, the longtime Democratic chairwoman in Clinton County, was a vocal critic then. Although she has vowed to stay neutral as a party leader, Pardee said she is impressed that a Clinton campaign staffer meets with her weekly to solicit advice. And she noted the campaign’s omnipresence at community events, such as an upcoming Thanksgiving food drive.

“They’re much more open and friendly,” Pardee said, “not at all as elite as they were last time.”

Anu Narayanswamy and Matea Gold in Washington contributed to this report.