SHENANDOAH, Iowa — Last month, Sen. Cory Booker warned that not making the December debate would be disastrous for his underdog presidential campaign, stretching his already limited resources to the brink and robbing him of crucial airtime just as many Democrats are deciding whom to support.

His urgent plea wasn’t enough. Booker failed to qualify for the Dec. 19 debate because of low poll numbers. He seems likely to miss the next debate, scheduled for Jan. 14 in Des Moines, too.

Even so, the New Jersey lawmaker is trudging along as several other candidates, including Sen. Kamala D. Harris (D-Calif.) and Julián Castro, have bowed out. It’s not because he’s seen a spike in the polls or a sudden influx of money. Rather, Booker’s campaign seems buoyed by the unusually large crowd of undecided voters, along with some die-hard supporters unconcerned about electability.

In tiny Shenandoah, a deeply rural farming community in southwest Iowa where the landscape is dotted with Trump flags, around 150 people turned out to hear Booker speak on New Year’s Day, packing so tightly into a small restaurant that some attendees were forced to peer through windows to catch a glimpse of the New Jersey senator.

It was one of three overflow events Booker held Wednesday across rural Iowa, in areas where Democrats tend to be more conservative.

“We have momentum,” Booker declared during a stop in Creston, Iowa. “I feel it. . . . We are going to surprise people.”

The crowds did not seem bothered that the candidate was registering 3 percent support among likely caucusgoers in a Des Moines Register/CNN/Mediacom Iowa poll from November, one of the last major polls conducted in the state. And they didn’t seem to care that he probably won’t make the January debate.

“I don’t think it matters,” said Scott Carpenter, an Iowa City mental health advocate who decided to formally endorse Booker last month with his wife, Leslie, after it appeared he would not make the December debate. “What matters in Iowa is relationships, your organization, your endorsements. . . . Those are the people who influence other people to go out and stand for you on a cold February night.”

The couple said they had personally urged Booker and his team to try to gain buzz in a different way: By booking bigger venues in hopes of attracting larger crowds that might match those turning out to see candidates like Pete Buttigieg, the former mayor of South Bend, Ind., who has commanded audiences around the state numbering around 1,000 or more in recent weeks.

“It’s time to go big,” Leslie Carpenter said. “We know he can, and I think he will.”

To be sure, Booker has a steep climb. The same four candidates — Buttigieg, former vice president Joe Biden and Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) — have been locked at the top of the polls here for months. While Booker’s team was hoping for a boost after Harris’s exit last month, a CBS News/YouGov poll of Iowa Democrats released Sunday found him at just 2 percent support among registered Iowa Democrats and Democratic-leaning independents.

While Booker raised $6.6 million in the last three months of 2019 — his best fundraising quarter yet — he lags far behind his competitors. If he can’t gain some ground in Iowa, it’s unlikely that he’ll have the support or resources to continue running.

That doesn’t seem to trouble Booker’s supporters.

In Iowa, a state where Booker has invested heavily and that is widely regarded as make-or-break for his campaign, the senator has rolled out more than three dozen endorsements since mid-December, including unexpected support from state and local elected officials and prominent activists who said they were moved to endorse when he was shut out of the debate.

Last month, after he criticized the lack of racial diversity on the debate stage, Booker raised enough money — including $1.7 million in a single day — to begin airing a 60-second biographical television ad in the state’s two major media markets, Des Moines and Cedar Rapids.

And though his crowds are smaller than those of some Democratic rivals, he is able to draw an audience. More than 300 people turned out for a pair of house parties near Des Moines on New Year’s Eve. About 30 percent of those who attended signed cards committing to support Booker at the Feb. 3 caucuses.

At his events last week, where Booker’s soaring and emotional stump speech led some attendees to burst into tears, many voters said they were still considering Booker.

Among those who gathered to hear him speak in Shenandoah was Howard Hart, a Page County farmer who said he had all but decided to caucus for Biden but had recently started to weigh other candidates just in case. He was impressed with Sen. Amy Klobuchar (D-Minn.), who visited here last month, and he liked Booker, too, with some reservations.

“I think very highly of him, and if I were to see support coalescing around him . . . I might do so also,” Hart said. “But he just doesn’t seem to be doing terribly well in polling.”

Booker readily acknowledged that he trails his rivals in fundraising and polls. In every appearance in recent days, he has sought to inspire his audience to look beyond those metrics, citing previous candidates like Jimmy Carter, John F. Kerry and Barack Obama, who he said emerged from low polling numbers to claim victory in Iowa.

“Don’t listen to the national polls. Listen to your heart, your gut, your spirit,” Booker said in Creston, his voice choked with emotion. “Caucus for me. I need you.”