IOWA CITY — On Joe Biden’s sixth day as a presidential candidate, he stood in front of a crowd at a brewery here and proclaimed that he would be in the state so often that Iowans would grow tired of seeing him.

“I promise you: No one is going to work harder to get the support and trust of the Iowa folks than I am this campaign,” he said. “Ninety-nine counties, here I come!”

Nearly seven months later, he has visited only about a quarter of those counties. He has been in Iowa fewer times than any of the other top-tier candidates, and he is spending much less on advertising than several of his rivals. And now, even as he retains a national lead in polling, he is falling behind in a state that doomed his campaign the last time he sought the presidency.

Biden’s campaign once shrugged off the potential impact of losing the caucus vote on Feb. 3, but concerns lately have grown about just how poorly he might do. Desperate to avoid a humiliating showing that might have broader repercussions, Biden is planning a renewed focus on Iowa, with an expectation that both he and his wife, Jill, soon will make the kind of extended trips to the state that other candidates have for months. They also have launched a new digital campaign and could have additional endorsements in the works.

“It’s a typical Biden campaign. It doesn’t yet have any excitement to it,” said Dave Nagle, the three-term former congressman from eastern Iowa who is neutral in the race. “The people with Joe are with Joe. They’re steady and reliable and will be with him. But he hasn’t been able to expand on it.”

Iowa always loomed as problematic for Biden — the state rewards not veteran politicians but new and fresh candidates who can organically excite and organize grass-roots movements, and it lacks significant numbers of Biden’s most loyal cohort, older black voters. But he is now threatened by an additional difficulty, the role he and his son Hunter have in the impeachment hearings underway in Washington, which may stretch into the Iowa caucuses.

Biden has a long and troubled history in the state. It was where he adopted the language and life story of a British politician in 1987 — triggering a plagiarism scandal that pushed him out of the 1988 race. Two decades later, in 2008, he carried none of the 99 counties, came in a dismal fifth place with just 0.9 percent of the vote, and immediately dropped out.

The shadow of his past failures has hung over this campaign, and a state that could showcase his strengths — an ability to win over people in small rooms — has instead exposed some of Biden’s biggest weaknesses.

Nagle, who has informally advised Biden’s teams in the past, compared him to George H.W. Bush in 1988 when the then-vice president was largely roped off from voters, while the eventual caucus winner, Sen. Bob Dole (R-Kan.), was far more accessible.

“There’s a formality to the campaign of the former vice president that doesn’t trade on his attribute of being, in person, warm and gregarious,” he said. “I’d like to see him in smaller circles, less prepared remarks, less podiums, and more engaging. He’s a warm person. But right now he’s coming across as kind of stiff, like a cutout rather than the real thing.”

Biden and his allies view the state as critical, with the candidate saying that Iowa holds “the keys to the kingdom.” He has already reserved $1.6 million in advertising for the final stretch, according to the media tracking firm Advertising Analytics. Advisers for the super PAC backing him recently held focus groups in Iowa to determine how best to buttress the campaign.

“Losing Iowa doesn’t mean we can’t win, but it makes winning the primary harder and more expensive,” his campaign manager, Greg Schultz, wrote in a fundraising appeal after a recent poll. “We still have time to turn this around . . . but not much.”

Biden’s difficulties were evident in a survey released Saturday night by the Des Moines Register and CNN. The poll showed South Bend, Ind., Mayor Pete Buttigieg gaining 16 points since September to lead the field. Biden was bunched in second with Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.); his 15 percent showing was less than half of what he commanded as the year began.

One of the most alarming signs for Biden was the indication that the once-warm views toward him have cooled. Biden was viewed favorably by 64 percent and unfavorably by 33 percent, a steady erosion from just before he entered the race, when 81 percent viewed him favorably and 15 percent unfavorably.

A separate CBS News poll showed slightly better news for Biden, with a four-way race at the top among him, Sanders, Buttigieg and Warren.

In that survey, 59 percent described Biden as “safe,” and 31 percent said he was “boring.” Sanders and Warren were most often described as “risky,” while Buttigieg was “down-to-earth.”

Biden’s less-than-concerted push for votes in Iowa has raised concerns among his partisans.

Among the 17 candidates in the race, he has done fewer events in Iowa than all but Tom Steyer and former Massachusetts governor Deval Patrick — a recent entrant — according to a tracker maintained by the Des Moines Register. Out of the 99 counties Biden promised to visit, he has 70 to go with about 10 weeks left before the caucuses.

This fall, several Biden rivals spent generously to make their case. From September through this month, Buttigieg poured $4 million into television and radio ads, while Sanders spent $3.8 million, according to data provided to The Washington Post by Advertising Analytics. Biden spent about $1.1 million — half of what entrepreneur Andrew Yang spent in the state. Warren spent $667,000.

Biden allies have blamed President Trump’s advertising campaign against him for his troubles, but Trump’s campaign spent less than half the amount that Biden did on television and radio ads, according to the data. The Trump campaign has also run ads on Facebook and Google, but those are difficult to separate geographically.

Biden’s $1.6 million advertising blitz will play out in December, January and February, according to Advertising Analytics. Warren, by contrast, has $2.6 million reserved.

The former vice president’s Iowa approach is based on an assumption that next year’s caucusgoers will be the usual crowd — mostly white, mostly older. His staff has hyperfocused on turning out senior citizens and working-class Democrats in rural and conservative parts of the state, especially those who voted for Trump.

But he lacks the organizational structure of some of his rivals, and as a result has made fewer inroads in places like Tama County, an area that is just like those Biden says he is primed to win.

“I don’t want to talk negative about anybody,” said Dave Degner, chairman of the Tama County Democratic Party. “But I would definitely point out that at least in our area, the Biden campaign has not put the same effort into having organizers here as some of the other candidates. . . . And I don’t understand why.”

The Biden campaign defends its organization, noting precinct captains have been recruited in all of Iowa’s counties. With 110 staffers and 25 field offices, Biden’s footprint is smaller than that of Warren, who has had staff in Iowa for almost a year, and Buttigieg, who ramped up his team beginning in late summer.

A more strenuous schedule, along with the heavy advertising, has given Buttigieg a boost among the same Obama-Trump swing counties on which Biden has focused.

That includes the Dubuque area, where Biden recently drew an audience of about 300 people at a local Catholic university, one of the biggest crowds of his Iowa campaign. But Buttigieg drew more than 800 people at his stop there in September, and Warren had roughly 615 at her stop this month.

Biden’s staff insists his audiences are intentionally kept small so the former vice president has time to meet and talk to attendees after his events.

Bruce Hunter, an Iowa state representative from Des Moines, fellow Democrat and longtime Biden friend, said it is in those human moments that the former vice president shines. He said he had encouraged Biden to not only spend more time in the state, but to do even smaller events.

“The big speeches are nice, but they are not necessarily going to get an individual to come out on a cold, snowy February night and commit three hours standing in line to openly commit to a candidate,” Hunter said. “That happens when you do the one-on-ones, when you talk to people personally.”

But in many cases, allies worry, Biden is winning few new converts.

“His main strength is also his biggest weakness, which is that he’s a known quantity. So I think a lot of people who originally supported Vice President Biden are continuing to support Vice President Biden,” said Steve Drahozal, chairman of the Democratic Party in Dubuque County, who is neutral in the race. “I don’t hear of anyone moving into his camp who wasn’t already there.”