At the massive state party event known for its catalytic effect on campaigns — it’s widely remembered as a turning point for Barack Obama’s Iowa fortunes in 2007 — Buttigieg captured the audience’s imagination, articulating a case for generational change.

“I didn’t just come here to end the era of Donald Trump,” Buttigieg said to a roaring crowd of supporters. “I’m here to launch the era that must come next.”

The South Bend, Ind., mayor’s speech offered an insight into his recent surge here, and why he is threatening to eclipse the former vice president in a state where Biden has been steadily losing ground since summer.

Ann Selzer, who heads the respected Iowa Poll, said her most recent poll showed 75 percent of those surveyed wanted a nominee who could inspire new voters to show up.

“Something I think is rather telling is those who want someone who represents a new generation of leadership,” Selzer said, noting that 57 percent of potential caucus-goers wanted new leadership versus 28 percent who wanted someone who had a long history of serving in government. “Who is that if it’s not Joe Biden?”

According to the New York Times/Siena College poll that placed Biden in fourth place in Iowa, the former vice president was showing little appeal among younger voters — only 2 percent of those under 45 years old said they planned to caucus for him.

Buttigieg, by contrast, has muscled his way into contention in the first-in-the-nation caucus state by steadily building crowds and rapidly expanding his presence in the state. In the last month alone, Buttigieg has doubled his staff presence while opening 20 offices across Iowa.

Matt Sinovic, executive director of Progress Iowa, one of the largest left-leaning advocacy groups in the state, said Buttigieg generated considerable buzz with a recent statewide bus tour. He starts another on Saturday. But the Indiana mayor is also swamping his opponents in digital advertising, something that’s been hard to miss in Iowa.

“I cannot overstate how many Buttigieg ads I see,” said Sinovic, pointing to data showing Buttigieg’s national digital spending numbers surpassing Biden almost five-to-one. “It’s just a massive outspending right now.”

Through his spending and organizing efforts, Buttigieg has managed to reshape the top tier into a 4-way contest that also includes Sens. Elizabeth Warren and Bernie Sanders.

Biden’s campaign, meanwhile, has been forced to scale down expectations of his performance here. He has already seen Warren overtake him in the polls and is also battling the grassroots energy behind Sanders.

“You might expect that a frontrunner is going to lose some ground as other candidates become more visible,” said Selzer. “It’s not just that there’s not enough numbers to go around. It’s that he’s not wearing well. It’s the trend, it’s the decline.”

Biden’s campaign announced on Friday a new round of digital ad spending in Iowa. And he’s opening a new office in the state, giving him 23 overall as well as 100 staffers. The campaign also notes an October fundraising bump as a sign they’re not losing momentum — the campaign said it had its best month to date online, raising $5.3 million from 182,000 donations, with an average donation of $28.

Democratic presidential candidate Pete Buttigieg speaks at the Liberty and Justice Celebration on Friday in Des Moines, Iowa. | Scott Olson/Getty Images

"We always knew this would be a very close race among the top candidates heading into Iowa, and that's what it is. But we're ready for it,“ said T.J. Ducklo, spokesman for the Biden campaign. “Donald Trump knows it too, which is why he and his allies continue to pour money into Iowa to stop Joe Biden."

For her part, Warren, who had perhaps the largest display of support in the Wells Fargo Arena, seemed to take a swipe at Biden, with whom she had tangled earlier Friday after he criticized her plans to fund Medicare for All.

“If the most we can promise is business as usual after Donald Trump then Democrats will lose,” Warren said. “Fear and complacency does not win elections. Hope and courage wins elections.”

The sniping between Warren and Biden came at the tail end of an eventful week in the primary where several campaigns appeared to be on life support and placed all their chips on Iowa.

Kamala Harris announced she’s slashing staff and redeploying resources here. Cory Booker is barely hanging on after making a desperate plea for cash in September. And on Friday, across from the arena where Democrats gather for the Liberty & Justice gala, Beto O’Rourke announced his departure from the race.

Tom Vilsack, a former Iowa governor and ex-Dept. of Agriculture secretary, shrugged off Warren and Buttigieg’s rising poll numbers in the state, saying neither have truly been tested just yet.

“She hasn’t had a worst day yet — none of these campaigns have except for Vice President Biden,” said Vilsack, who served with Biden in the Obama administration and hosted a house party for him in July. “And the thing about Biden is he’s still standing. The question is will the rest of them still be standing after they’ve taken a punch? We’ll see.”