Iowa is where Pete Buttigieg, still a single-digit candidate nationally, is surging, where Elizabeth Warren has overtaken Joe Biden and where the former vice president — still leading nationally — is at risk of getting cut down. And it is serving as the fulcrum for a host of other candidates — among them Sens. Cory Booker and Kamala Harris — who hope to leverage their performance across the state’s 99 counties into relevance in the states that follow.

“I can’t keep up with all of them,” Vicky Brenner, liaison for presidential candidates in Madison County, said on her way into a Democratic Party dinner in Indianola on Sunday night, after a weekend that drew all of the major presidential candidates to the state.

Earlier this year, the prospect of a not-quite-so-important Iowa appeared relatively high. In an effort to meet debate qualification requirements, candidates put a heavy focus on national polls and small-dollar fundraising, fanning out across the country in a scramble for donations, TV hits and social media impressions. The frontloading of the primary calendar further destabilized the map. With massive delegate hauls in California and Texas coming right after the first four nominating states, well-financed candidates began drawing plans for a run through Western and Southern states.

In Iowa, said Tom Courtney, a former state senator and now co-chairman of the Des Moines County Democrats, “it wasn’t eight years ago that people were saying, ‘I want to have a primary … let’s just do away with the caucus.”

“Now, all of a sudden, they aren’t,” he said. “A lot of people are understanding we don’t want to lose this first-in-the-nation status.”

The tilting of the campaign back toward Iowa in recent weeks was consecrated with a rush of activity in recent days.

Harris and Booker, who need to perform well in South Carolina, may not even make to that state without a strong finish in Iowa. And two Northeastern senators, Elizabeth Warren and Bernie Sanders, maintain a regional advantage in New Hampshire, where they stand with Biden atop recent polls. That is not only lowering expectations for any other candidate in New Hampshire, but making it less efficient for them to expend time and resources to compete there.

“The candidates who don’t have a natural allegiance to New Hampshire or aren’t perceived to be strong in South Carolina — i.e. everybody but Biden — this state does take on more prominence than it has before,” said Dave Nagle, a former congressman and Iowa state Democratic Party chairman.

And Biden, while dominant in South Carolina, runs a risk of shedding some of that support if voters there see him flop in the first state to vote.

“If this race were planted in 2008, Joe Biden probably could get away with a bad Iowa, a bad New Hampshire and come back and win Nevada and South Carolina,” said Andrew Turner, a Democratic strategist in Iowa who supports Booker. “But what you [the media] are about to do with that man once he gets fourth in Iowa … This is every staffer’s nightmare.”

Turner said, “You guys are going to light into whoever does poorly in Iowa. You’ll get some staffer on background to be like, ‘The campaigns’ over,’ and it’ll just be crippling.”

Biden fell to fourth place in Iowa in a New York Times/Siena College poll Friday, and as he campaigned through Iowa, his supporters were left to defend his prospects. Harold Schaitberger, president of the International Association of Fire Fighters, told reporters at a fish fry in Cedar Rapids that “enthusiasm” is different from “commitment.”

Invoking New Hampshire, Schaitberger said enthusiasm is “easier to be able to capture” in a primary state with its relatively simple voting procedures. A caucus state such as Iowa, he said, is “so unique.” Biden has about 100 staffers in Iowa and more than 20 offices.

Schaitberger said, “I just think we’re where we need to be.”

But with Biden’s weakening standing in the polls, his opponents sense a wider opening than ever before in Iowa — and one that could carry over into later states.

While Sanders was addressing a small gathering at an arts center in Waterloo on Sunday, Faiz Shakir, his campaign manager, said that because Iowans take their caucus process so seriously, “I actually think there’s a lot of Californians and a lot of Nevadans and a lot of South Carolinians who want to see who Iowans have decided,” and while not necessarily following Iowa’s lead, “give deferential weight” to the caucus result.

Sanders’ campaign said it is ahead of schedule recruiting volunteers and staffers in the state, with Shakir predicting the campaign will have at least 1,000 staffers and volunteers knocking on doors in Iowa by the time of the caucuses.

Doug Herman, a lead mail strategist for Obama’s 2008 and 2012 campaigns, described candidates’ intense focus on Iowa this year as the evolution of a years-long convergence in electoral politics in which “state contests, which used to be hyper-localized affairs, became national fodder for cable news.”

Iowa stands out especially this year, he said, because “New Hampshire has its favorite son-daughter thing,” and because “South Carolina and Nevada are far enough down the path that they’re going to be significantly and determinatively impacted by the outcome in Iowa.”

Last week, Sen. Kamala Harris’ campaign began laying off aides at her Baltimore headquarters and redeploying staff to Iowa. At an event in Indianola, an adviser to Julián Castro said that in Iowa, “the ground is absolutely moving under the frontrunners right now.”

For long-shot contenders such as Castro, Colorado Sen. Michael Bennet or former Rep. John Delaney, who has been toiling in Iowa for more than two years, a surprise fifth- or sixth-place finish in Iowa could generate enough interest to at least briefly breathe life into their campaigns.

And the breadth of candidates counting on that is a self-perpetuating, complicating factor for the entire field as it approaches the caucuses.

“With the [large] number of candidates, you don’t need a significant percentage to win,” said former Iowa Gov. Tom Vilsack, who briefly ran for president in 2008. “So, the more people you touch, the more people you talk to, the more people you have a connection with, potentially, you may be able to make sure they show up to the caucus.”

Vilsack said that in a normal year, “if you can get thirty or forty or fifty thousand people, that might not be sufficient.” This year, he said, that kind of showing might prove enough “to get your ticket punched out of Iowa.”