ANKENY, Iowa — To hear Kamala Harris tell it, her trip to Iowa this week was all about urging Democrats to get to the polls and vote early. With just over two weeks to go before the 2018 midterm elections, the California senator insisted her multi-stop swing across the first presidential battleground state had nothing to do with any national ambitions.

"Please vote in the next 15 days and get all your friends to vote," Harris replied when a reporter asked on Monday if a presidential bid might be in her future.

Still, Harris's trip represented a breakthrough in Iowa — signaling the 2020 contest to challenge President Donald Trump had moved into an important and more urgent phase for what is expected to be a large and wide open Democratic field.

Harris and other top-tier potential 2020 hopefuls had until recently been avoiding of places like Iowa and New Hampshire, leaving those attention-grabbing early presidential voting states to lesser-known Democrats eager for the exposure.

But with the list of candidates eyeing a bid for the nomination already long and growing, the party's best-known figures are finally stepping into the spotlight.

"There's a contest for talent," Iowa Democratic strategist Matt Paul said, noting there are only so many experienced presidential campaign operatives in early states and they are typically swept up quickly.

"Candidates need infrastructure, an activist list, a donor list. Those take time to build," he added.

Privately, many believe that Iowa's small size and its quirky and challenging caucus system aren't built to handle the large number of Democrats eyeing a presidential bid. And while presidential candidates of both parties in the past have experimented with skipping the Hawkeye State altogether to focus on other early contests, none has done so and gone on to win nomination.

The path to victory, for better or worse, necessitates a major investment in Iowa.

New Jersey Sen. Cory Booker recently made his first trip here, headlining the state Democratic Party gala and campaigning with Democrat J.D. Scholten, who challenging Iowa Republican Rep. Steve King.

Sen. Kamala Harris greets supporters in Des Moines, Iowa, on Oct. 22. KC McGinnis / Reuters

Both Booker and Harris, as members of the Senate Judiciary Committee, saw their profiles rise significantly after last month's contentious hearings to confirm Supreme Court nominee Brett Kavanaugh. Minnesota Sen. Amy Klobuchar, another prominent Democrat on the Judiciary panel eyeing a potential White House campaign, hasn't visited Iowa since 2017, focusing for now on what's expected to be an easy re-election next month.

Former Housing Secretary and San Antonio Mayor Julian Castro, one of the party's leading Hispanic voices, made a visit to Iowa last month to do a fundraiser with young Democrats. Another top-tier Democrat, New York Sen. Kirsten Gillibrand, has so far stayed out of Iowa but ventured to New Hampshire last week to campaign for Democratic candidates in the state.

Massachusetts Sen. Elizabeth Warren, who has said she would take a "hard look" at running in 2020 and who released a DNA test last week to confirm Native American ancestry, has stayed out of both Iowa and New Hampshire for now but has deployed staffers to both states.

Former Vice President Joe Biden and Vermont Sen. Bernie Sanders, arguably the highest profile potential Democrats, are taking opposing tacks. Sanders, who narrowly lost the Iowa caucuses to Hillary Clinton in 2016 before defeating her in a landslide in the New Hampshire primary, has been in and out of Iowa repeatedly, most recently last weekend as part of a nine-state midterm campaign swing.

Biden, for his part, has stayed away from both Iowa and New Hampshire, campaigning for candidates in presidential battlegrounds like Ohio and Florida and focusing considerable attention on South Carolina, the first in the south primary state. Biden's last bid for the Democratic nomination, in 2008, was snuffed out in humiliating fashion in Iowa, where he received less than one percent of the caucus vote.

A handful of Democratic governors have made appearances in Iowa over the last year, including Colorado's John Hickenlooper, Washington state's Jay Inslee and Montana's Steve Bullock. All have said they are considering a 2020 run. California Rep. Eric Swalwell, a visible member of the House Intelligence Committee looking into potential ties between Trump's 2016 campaign and Russia, has been to the state several times, while Maryland Rep. John Delaney, who has already announced his candidacy, has practically moved to Iowa.

At an event in Indianola where she shook hands and posed for selfies with activists, Harris told reporters she welcomed the kind of retail, up-close-and-personal politicking Iowa voters expect of presidential candidates. She recalled going door to door for President Barack Obama ahead of the 2008 presidential caucuses, which won and which launched him to the Democratic nomination that year.

"You'd knock on a door, people would invite you in, you'd sit down, have a cup of coffee and have a conversation," Harris said. "There's nothing more important than engaging with people one on one."