CEDAR RAPIDS, Iowa — In the early state where field organization has traditionally mattered the most, Sen. Cory Booker and Sen. Elizabeth Warren have quietly and patiently concentrated their resources toward building grassroots machines designed to power them on caucus night.

It showed here on Sunday as 19 Democratic presidential candidates converged for the first time in one venue to make their five-minute pitch to the party faithful. The gathering, designed to honor Iowa Democrats in a Hall of Fame dinner, offered the first glimpse of a sprawling Democratic primary field — and the organizational strength and enthusiasm each campaign could muster.

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Booker and Warren weren’t the only presidential hopefuls to stand out. The senator from next door in Minnesota, Amy Klobuchar, also put on a show of force both inside and outside the Cedar Rapids Doubletree Hilton Hotel, where the dinner took place.

But Booker was among the first candidates to ramp up early in Iowa and it enabled him to flex his muscles Sunday, one day after a new Des Moines Register/CNN/Mediacom survey of likely Iowa caucusgoers placed him at just one percent in the crowded field.

When Booker took the stage before the 1,400-person crowd, dozens of supporters rose to their feet and lifted “Cory Booker 2020” signs that lit up in the dark.

“Nobody has seen anything like this,” Booker told POLITICO afterwards, in reference to the raucous 19-candidate gathering.

The New Jersey senator was the first, drawn at random, of the candidates to speak. Each was given five minutes to boil down their stump speech and at times, in an Academy Award-like manner, candidates were cut off with music playing over their speeches.

“You just got to go up there and let people hear you and feel you,” Booker continued. “If you can accomplish that — and I heard some big responses from people who weren’t part of my team there. I just wanted to go up there and frame the election as I see it.”

The crowd reactions and engagement offered evidence of which candidates were still working on their introductions to Iowa activists and which had already established a rapport.

Warren barely got out the words: “I got a plan” before the crowd erupted. At one point they chanted “Warren!” “Warren!”

Klobuchar, who drew a healthy turnout at a mini-rally before the event, also drew cheers — and laughter — when she sold herself as the candidate who knows the heartland because she’s from the heartland.

“I can see Iowa from my porch,” she joked.

Penny Rosfjord, a former Woodbury County chair, said the day made clear which candidates were establishing traction at the grassroots level.

“I feel like the people who are doing well in Iowa — I’m not talking about polls, I’m talking to other activists — are the people who are organized on the ground in campaigns. Warren, Booker,” said Rosfjord. “[Kamala] Harris has a good campaign. She’s still fresh to getting boots on the ground. Beto [O’Rourke] is one of the good campaigns, all their staff isn’t out yet.”

Remarks from lesser known candidates and late entrants into the Democratic field — among them, New York City Mayor Bill de Blasio and Colorado Sen. Michael Bennett — received more tempered responses from the audience.

But O’Rourke, the former Texas congressman, closed out the speeches with loud cheers and a standing ovation. Though he set up shop in Iowa long after Warren and Booker, O’Rourke has poured resources into the state and is developing a robust ground game. This weekend, O’Rourke opened up a Cedar Rapids office in what marked his fifth trip to the state and the first one accompanied by his wife, Amy.

“We’re all in this together for the same purpose and cause, and we’re all going to do our best to distinguish ourselves,” O’Rourke said in an interview after his remarks.

O’Rourke said he focused his remarks on Sunday to stress “bold” proposals, including registering 50 million voters in automatic and same-day registration. “Not only is that a bold and necessary proposal to get this done, it’s also reflective of how I’ve lived my life, how I’ve served in Congress, how I’ve campaigned across Texas.”

Several campaign representatives said they viewed the day as the first test to demonstrate their viability and ability to turn people out to the Feb. 3 caucuses. That’s why both inside and outside the venue, a competition played out among campaigns to convince potential caucus-goers that they had captured grassroots enthusiasm.

There were flashing campaign signs, fluorescent yellow glow sticks, giant banners, chanting supporters and even bagpipes, courtesy of former Maryland Rep. John Delaney. A stream of supporters clad in yellow shirts lined the street outside the event to support Kamala Harris. Inside, they attempted a show of strength by noisily waving yellow glow sticks before Harris took the stage.

Front-runner Joe Biden, who led the crowded Democratic presidential field in the Des Moines Register/CNN/Mediacom poll, had virtually no presence at the party event. His campaign said the former vice president missed the dinner due to his granddaughter‘s high school graduation.

For his part, Bernie Sanders took a different path than many other contenders Sunday, marching with fast-food workers through the center of town demanding a $15-an-hour minimum wage.

“I understand there are some well-intentioned Democrats and candidates who believe the best way forward is middle-ground strategy that antagonizes no one. That stands up to nobody and that changes nothing. In my view that approach is not just bad public policy, but it is a failed political strategy that I fear could end up with the reelection of Donald Trump,” Sanders said.

“The American people want change. They want real change and we have got to provide in that change.”