BURLINGTON, Iowa — As Senator Cory Booker swept through Iowa on a four-day visit over Memorial Day weekend, he called on his often overflowing crowds to approach the presidential primary campaign through a new paradigm.
“This election, I get a little frustrated, I have to admit to everybody,” he told a crowd of about 200 at a union hall in Burlington on Saturday. “A lot of people want to say this election is just about getting rid of Donald Trump. That’s the floor, not the ceiling.”
Mr. Booker was seeking to flip the national narrative, drawing voters to the layered chapters of his political biography: the telegenic liberal mayor of a downtrodden New Jersey city who went on to become a senator and an adversary of President Trump. But the sheer breadth and diversity of the Democratic field have weighed on Mr. Booker, one of his party’s long-rising stars, who had been seen as a possible presidential candidate since he burst onto the scene two decades ago.
Yet his presidential résumé mirrors that of other rivals who are ahead of him in the polls. The sensible, Rhodes scholar, get-things-done mayor? Shared with Mayor Pete Buttitgieg of South Bend, Ind. The groundbreaking African-American candidate? Taken by Senator Kamala Harris of California.
The trip to Iowa was Mr. Booker’s fourth of this campaign, evidence of the need for a strong showing in this first caucus state for any hope of a successful run through to South Carolina, where Mr. Booker is hoping for a victory. The entrance of former Vice President Joseph R. Biden Jr. into the race puts added pressure on Mr. Booker, especially competing for black voters — a major piece of the Democratic constituency in the South, and a group that has largely supported Mr. Biden in early polls.
On the trail, Mr. Booker is still campaigning with an ebullient style, recording selfie videos for voters and cracking self-deprecating “dad jokes” at every stop. He even broke briefly into song during an interview, singing a few bars of “My City of Ruins” by Bruce Springsteen.
But stuck in the low single digits in both national and early state polls, with a middling small-dollar fund-raising operation, he has started to sprinkle his unity-themed stump speech with some slight contrasts to other Democratic candidates.
“I’m one of those Democrats to say we need to start doing things that make people’s lives better, because Democrats have done things that have made people’s lives worse,” Mr. Booker said at a house party in Newton, referring to the 1994 crime bill that Mr. Biden supported while he was in the Senate, and which experts say contributed to mass incarceration.
And in calls for party solidarity, he offered a veiled critique of the hesitance of Senator Bernie Sanders of Vermont to endorse Hillary Clinton in 2016.
“I hope that one of the questions you ask every single candidate is, if you’re not the person, that you will commit to us that you will double down and support the person who is the nominee,” Mr. Booker told the crowd in Newton. “I saw that movie in 2016. I don’t want to relive it.”
Though he claims to try to avoid direct attacks on President Trump — “The more attention we give him, the more oxygen he takes,” Mr. Booker said — he has increased his criticisms, including taking a generational swipe at him as he looked ahead to the stakes of the climate change fight “20 years from now, when I’m the age of this current president.”
To hear Mr. Booker describe it, he is “pumped” about his campaign’s status, a slow-but-steady strategy espoused by the “Brick by Brick” slogan seen on signs at a town-hall-style event in Burlington on Saturday and on his campaign social media accounts.
“I think if you look at the fundamentals of what has won past competitive Iowa primaries, we are doing extraordinarily well,” Mr. Booker said in an interview. “The folks who know the politics in the state will unequivocally tell you we have the best organization on the ground.”
While supporters in Iowa are confident in his message, some are perplexed at his stagnant polling.
“I don’t know if it is because the message of love, and some people don’t necessarily connect to that,” said Rachelle Chase, 55, from Ottumwa, who has written two books about the Buxton coal mines, where Mr. Booker’s great-great-grandparents worked. “But I think what appeals to me is that he’s being authentic.”
His focus on Iowa, with 30 events held as of Sunday and a staff of 50 in the state, and his pledge to unveil a “Marshall Plan” for rural America could help him build momentum.
“These are areas that have experienced a lot of difficult economic times,” said Representative Dave Loebsack, who accompanied Mr. Booker on Saturday and represents an Iowa district Mr. Trump won in 2016. “I think just listening to them and talking to them along economic lines is the most important thing candidates can do.”
Mr. Booker made a splash nationally with his sweeping gun reform policy, and earned kudos from many voters this weekend for his vocal response to the wave of new state bills restricting abortion. And he teased thoughts on regulating social media companies, taking direct aim at criticisms that he has been too cozy with big tech.
“I think that having better control of your own data and information is really important, and restricting the ability of platforms to be able to use your data for their profit,” Mr. Booker said in an interview. “This is a space where we need to regulate, and having more transparency in that area is something we need to regulate.”
His flatlining in the national polls has not helped an already struggling small-dollar fund-raising network; just 16 percent of his donations in the first three months of the year were $200 or less. Instead, Mr. Booker has kept a steady pace of high-dollar fund-raising events, and his campaign has roughly two dozen fund-raisers across six states already on the books for the next month.
Though he pledged in an interview to release the names of his bundlers — supporters who gather donations from friends and business associates — he said he currently would not allow pooled news media coverage of his fund-raisers as Mr. Biden has.
Mr. Booker did get one small-dollar boost on Saturday. While touring the flood damage in downtown Muscatine, Mr. Booker was stopped by two local farmers, Garry and Carolyn Reid. They farm 20,000 bushels of corn and soybeans per year, and said they had lost 85 cents per bushel as a result of Mr. Trump’s trade war.
Since then, Mr. Reid said, the federal government deposited $200 into their bank account from an emergency fund. So Mr. Reid, 83, took $25 from that and donated it to Mr. Booker’s campaign.
“You have no idea how much this encourages me,” Mr. Booker said.
“Well,” Mr. Reid replied, tugging on his suspenders and offering a smirk, “it’s going to take more than that.”