COLUMBIA, S.C. — Mayor Pro Tem Tameika Isaac Devine has been a fan of Sen. Cory Booker since his days as Newark mayor. An admirer of his consensus-building style, she invited him into her home and said he “electrified the room.”

But she has not yet endorsed his campaign for president, and when asked why, she talks about her friends who worry his “Rise Up” message, a call for national healing and inspiration, would be a poor fit for the general election.

“He’s not a safe choice for some people, although people like what he has to say,” Devine said. “It’s not personally about him as much as people feel like they have to have someone who is going to win and beat Donald Trump.”

As he struggles with low-single-digit polling and the prospect of missing the cut for next month’s debate, Booker has become a symbol for the harsh reality of this year’s nominating process. It is just not enough to win plaudits for performance, as he has after multiple events, or to execute a clear campaign strategy. In the shadow of Trump’s potential reelection, Democratic voters have become focused on winning and are unforgiving with their doubts.

Booker has sought to answer that concern by preaching the power of empathy. He appeals to white Iowa and New Hampshire voters by talking about the problems of inner cities and poverty. He has confronted Trump by explaining his compassion for his supporters. And unlike other campaigns that have pivoted on message and policy, he has made clear he will not change his strategy to win.

“I literally had someone say, ‘How are you going to beat Donald Trump with love, Cory?’ ” he said after an event Friday in New Hampshire, placing himself in the legacy of the Rev. Martin Luther King Jr. “And I laughed. You don’t know our history! That’s how we always win! King said, ‘Darkness can’t drive out darkness; only love can do that.’”

Everywhere Booker goes these days — in press gaggles and at candidate forums, in Iowa church pews and New Hampshire town halls — he is followed by questions about why his bid is still stuck in the low single digits.

The senator from New Jersey’s stock answer is that he just needs more time, a few more donors — “Please go to corybooker.com,” he pleaded at the last debate — and the wisdom to remember that past Democratic nominees Barack Obama and John Kerry were trailing at this point in their primary campaigns.

But in moments of candor, he can be more reflective. “This is the challenge,” he told one loyal volunteer last month who had asked at a town hall in West Des Moines what more she could do to get his name out there.

He even betrayed some frustration at the debate last week about his ability to break through. “I happen to be the other Rhodes Scholar mayor on this stage,” he said, in a dig at the attention that has been drawn to South Bend, Ind., Mayor Pete Buttigieg.

The broader dilemma he faces has bedeviled more than a dozen campaigns this cycle. Those out of the top tier struggle as they seek even minimal attention, and without attention they cannot reach the top tier.

“Until voting starts, the way voters can determine viability is through things like fundraising, polling and earned-media coverage,” said Meredith Kelly, a Democratic strategist who advised the short-lived campaign of Sen. Kirsten Gillibrand (N.Y.). “And if you aren’t considered worthy of going viral, worthy of being a top-tier candidate by cable news and big donors, then it becomes this self-fulfilling cycle.”

Booker’s campaign manager, Addisu Demissie, told The Washington Post that Booker’s success has often been unfairly contrasted with the high expectations set by a political establishment that long saw him as a rising star.

“We have a high bar to clear,” he said Saturday. “And the reality is he’s been clearing it, particularly in the early states. But the metric that the press has been paying the most attention to is polling — not endorsements, not favorability, not consideration. We’re winning by those metrics. It’s only the horse race that we’re not winning, yet.”

Booker’s campaign message, a departure from the rest of the pack, has so far failed to overcome the challenge, although he says he has attracted a devoted following. His fundraising jumped after Wednesday’s debate — his campaign anticipated it will have collected $1 million by the end of the weekend — and he points to relatively high favorability in recent Democratic polls.

His announcement video, scored to a drum-line beat, showed him walking the graffiti-strewn streets of Newark, yelling “What’s up?” to a passerby. An early endorser of Medicare-for-all, he has campaigned on legalizing marijuana and expunging the records of the mostly nonwhite Americans with minor drug convictions.

This was a departure from the more buttoned-up approach he took in his first Senate campaign, a 2013 special election, in which he ran ads that showed him in a suit and tie, speaking in glass-walled conference rooms, with graphics about bringing in “new business” and a voice-over that promised innovation and to “reach for new answers.” As a senator, he has been known as a more moderate Democrat, earning financial support from former New York mayor Mike Bloomberg, supporting charter schools and voting against a bill to encourage the importation of drugs from Canada.

As a presidential candidate, by contrast, he has more closely identified with the struggles of urban populations. Like Sen.Kamala D. Harris (Calif.) and former housing secretary Julián Castro, Booker has argued that the party needs to focus on black voters to increase turnout in cities like Detroit and Philadelphia in the general election. But the positioning has yet to earn any of them a spike in support among black voters, who continue to back former vice president Joe Biden in polls.

Interviews with black voters in South Carolina found high praise for Booker’s message. But those same voters repeatedly stopped short of supporting him.

“He may be eloquent and he may be educated, but will they vote for him?” asked Wilma Doyle, 74, a retired schoolteacher from Greenville who said she likes almost everything about Booker. “He is good, but I don’t think he has the best chance.”

David Gaston, 75, a Vietnam veteran from Greenwood, said he likes Booker personally, but still ranks Biden and Sen. Elizabeth Warren (Mass.) ahead of him in his preference for a nominee.

“Sometimes, you’ve got to fight. When you’re in a war, you’ve got to fight,” Gaston said. “Biden has the knowledge of how the world works. Elizabeth Warren is a fighter.”

Booker has approached the campaign, instead, as a moment for national inspiration and spiritual rebirth.

“Love is not sentimentality,” Booker said Friday at a University of New Hampshire town hall in Durham. “Love is service. Love is sacrifice. Love is saying, ‘Hey, if your kids don’t have a great public school to go to, my kids are lesser off.’ Love says that injustice anywhere is a threat to justice everywhere.”

He hugged an audience member for asking a question about poverty.

To make the cut for the December debate, Booker will need to score 4 percent or higher in four party-sanctioned polls over the coming weeks. He has so far failed to reach that level in any party-sanctioned poll published since mid-October.

Even if he does not make the cut, he has vowed to continue his campaign, with a pathway that remains focused on Iowa. He has devoted significant resources to the first-voting state, hiring an early statewide staff of 50, including several aides who got tattoos of the slogan “We Rise” in Booker’s handwriting.

“Booker could actually do incredibly well here. He has a great organization, has a great staff. They’ve got great endorsements,” said Grant Woodard, a Des Moines attorney and former Democratic strategist who is unaffiliated in the race. “But there’s just so much noise with all these other candidates running.”

At his second New Hampshire event Friday, 125 people overflowed a brewery in downtown Portsmouth, where organizers had planned for 50 people.

After Booker finished speaking, Greg Norris, a marketing executive, hung in the back of the event space with a beer as his 18-year-old son waited in line for a selfie with the senator.

“I think his message of inclusion is right on,” Norris said about his first time seeing Booker. “I’m very surprised that he hasn’t gotten the traction. When you look at just the qualifications, the way he speaks, a level of intelligence, the education, the experience, I’m really surprised, relative to the other candidates.”

But Norris still wasn’t sold. He said he was not yet ready to say he would vote for Booker.

Amy B Wang in New Hampshire and Holly Bailey in Iowa contributed to this report.