The top tier of the prospective Democratic field in the 2020 presidential race is making its way to Iowa ahead of the first-in-the-nation caucuses that already are being described as more important than ever.

The caucuses, set to take place on Feb. 3, 2020, could give a much-needed early boost to more than one candidate in what is expected to be a crowded field that could include two dozen people.

“If you’re an underdog candidate, you’ve got to be in the top three to break out,” said Pat Rynard, who runs the political website Iowa Starting Line.

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Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.) over the weekend visited the Hawkeye State for the first time since the 2016 campaign. He appeared at a string of events in subsequent days to campaign for 2018 midterm candidates.

“My chief of staff wouldn’t let me come up to Iowa because people would talk about presidential stuff,” Booker joked to a crowd in Boone on Monday.

Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.) is expected to make appearances for midterm candidates later this month over the course of several days.

Sen. Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE (I-Vt.), who narrowly lost the caucuses to Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE in 2016, is set to visit Iowa later this month. It’s one of nine states he’ll visit while campaigning for Democratic candidates in the midterms.

A few others seen as top candidates if they choose to enter the race, including former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE and Sen. Elizabeth Warren Elizabeth WarrenDimon: Wealth tax 'almost impossible to do' CNN's Don Lemon: 'Blow up the entire system' remark taken out of context Democrats shoot down talk of expanding Supreme Court MORE (D-Mass.), have no current plans to go to Iowa.

And one underdog candidate, Rep. John Delaney John DelaneyCoronavirus Report: The Hill's Steve Clemons interviews Rep. Rodney Davis Eurasia Group founder Ian Bremmer says Trump right on China but wrong on WHO; CDC issues new guidance for large gatherings The Hill's Coronavirus Report: Kansas City Mayor Quinton Lucas says country needs to rethink what 'policing' means; US cases surpass 2 million with no end to pandemic in sight MORE (D-Md.), is practically living in Iowa. Delaney, the only Democrat to have officially entered the race, has already visited the state’s 99 counties and is running advertisements as part of a strategy of jump-starting his campaign with a strong finish in Iowa.

In 2016, Clinton and Sanders lapped a relatively small field, and the race for the Democratic nomination was clearly a two-candidate contest.

The next race is likely to be different, and big-name and underdog candidates alike will be looking for a major jump start from the Hawkeye State’s voters.

“Iowa will play its usual role at winnowing down the field,” predicted Jerry Crawford, a longtime Democratic Party operative in the state who served as an on-the-ground political fixer for Clinton.

Another reason many Democrats think Iowa will have outsize importance in 2020 is that California’s primary will take place much earlier in the next presidential cycle.

While the Iowa caucuses and New Hampshire and South Carolina primaries will all take place first, California has moved its contest up to March.

Given advertising costs in the state, it will be important for candidates to emerge in Iowa to survive through California.

“You’re immediately going into the most important state to campaign in so unless you’re one of those candidates with a ton of independent money you’re not going to be able to create that media buzz,” said Rynard.

Most of the big-name potential Democratic candidates have sought to not advertise possible presidential ambitions with stops in Iowa.

It’s one of the things that made Booker’s comment about his staffer not letting him go to Iowa both funny and telling.

“The reason they’ve been coy and shy until now is that they don’t want to stick their heads out there before they know the best way to reach Iowa voters,” said Steffen Schmidt, a political science professor at Iowa State University.

He added that “conventional wisdom also shows that you can’t be out there too early.”

A poll last month by David Binder Research asked 500 Iowa caucusgoers whom they most wanted to see run for president among Democrats. Biden led with 21 percent, compared to 8 percent for Sanders, 7 percent for Warren, 6 percent for Harris and 5 percent for Booker.

Rynard said reaction to Booker this week was “pretty impressive.”

“It felt like something I haven’t seen yet this cycle,” he said. “It felt like the last week of a campaign.”

Iowa is as important as ever, Rynard maintains, and he cautions candidates to forgo it at their own risk.

“Every year where there’s probably some way to get the nomination but it seems awfully risky, so why risk it?”