DES MOINES — When Sen. Kamala D. Harris arrived in Iowa for the first time since her attention-grabbing debate performance, she did so with a revamped stump speech and almost double her previous forces in Iowa and New Hampshire, all part of a retooled approach her campaign hopes will ensure her breakout moment fosters lasting momentum.

Harris’s campaign team says many of these changes were planned far earlier. But they are coming at a pivotal moment — just after the first Democratic debate and as the candidates are separating into more distinct tiers. Harris’s push to sharpen her message and expand her operation is shifting the overall dynamic of the contest for the Democratic presidential nomination.

In returning to Iowa this week, Harris abandoned a stump speech that centered on the vague notion of “speaking truth” and offered little clear reason for her candidacy. Instead, she is promoting the idea of a changing country — “our America” — in contrast with what she characterizes as President Trump’s effort to take the nation back into the past.

She has also begun embracing her controversial history as a prosecutor instead of shying away from it, telling voters that her record of taking on predators (she includes in that “big banks, big pharmaceutical companies, transnational gangs, and more”) equips her to prosecute the “predator living in the White House.”

And after months of criticism from Democrats in Iowa and New Hampshire who said they felt she had not made them a priority, Harris has hired 35 additional staffers in Iowa in recent days, raising her total in the state to about 65 — one of the largest teams on the ground here, according to people familiar with Iowa campaign operations. She also hired 25 additional staffers in New Hampshire.

“I think, early on, she didn’t have much ground game in Iowa in general,” said Scott Putney, the chairman of the Pottawattamie County Democrats, who spoke before Harris at a campaign picnic in Council Bluffs. But now, he said, “they’ve got tons of organizers on the ground. You feel it.”

Harris has also made a less-tangible shift. In challenging former vice president Joe Biden on segregation and busing during the debate, the U.S. senator from California identified herself more clearly with the liberal activist wing of the party, a move that has boosted her in the primary polling but could carry risks with centrist voters.

At her appearance at a brewery in West Des Moines, the questions were not about race or her conflict with Biden, but about the importance of defeating Trump. Several voters said her assertive performance at the debate had convinced them that she could take on the president.

“That’s what we have to do — beat Trump,” said Don Palmquist, 79, a retired carpenter from the rural town of Stanton, Iowa. “She came across as somebody that’s very confident, and that’s going to be one of the requirements to do the job this time.”

Harris’s stepped-up presence in Iowa is a major change. Since her campaign began, Democratic activists here had complained that she hardly visited and did not have much of an organization in the state. Some had concluded that her strategy was to avoid expending resources in largely white Iowa and New Hampshire and instead hope to catch fire in states with more African American voters.

One of the first questions Harris fielded as she spoke to the news media Wednesday came from an Iowa journalist who asked how she would convince Iowans that she cares about the state. She said that she would continue to show up.

Her aides say her strategy always was to make a more concerted push in Iowa and New Hampshire over the summer. The Iowa buildup, for example, had been planned since March, they say, and she spent much of the past few months focusing on fundraising so she could fund the staff expansion.

More time spent on fundraising meant less time for trips to Iowa. Now, she will have made two trips to Iowa in 12 days and could make a third before the month is up.

But circumstances on the ground have changed as well. Biden’s lead among African American voters since he joined the race has proved more durable than many strategists expected, increasing the pressure on Harris to perform well in Iowa and New Hampshire to give her momentum as she heads into South Carolina and other Southern states.

In 2008, Barack Obama struggled to win over African American voters in the South — until he won in the Iowa caucuses, which showed black voters that he could capture majority-white states.

Until now, political strategists in Iowa have said Sens. Elizabeth Warren (D-Mass.) and Cory Booker (D-N.J.) had the biggest operations in the state. Many now say Harris has joined their ranks.

The Harris campaign hosted a barbecue Thursday beside the Missouri River, drawing a robust 500 people in a conservative part of the state. Many said they did not hold the infrequency of Harris’s visits to the state against her.

“It takes a long time to build a campaign up, and it’s a marathon, not a sprint,” said Derick Barnes, 30, an area resident who attended the barbecue. “But I think she’s going to be giving Iowa its due.”

At the same time, lingering questions from the debate, and from the early part of her campaign, have followed Harris through the state in recent days.

In the aftermath of her criticism of Biden for his opposition to court-ordered busing in the 1970s, she has fielded days of questions about her own stance on the issue.

After several days of varying answers, she was forced to clarify again Thursday, ultimately saying she would support federally mandated busing if a particular school district was resisting integration — but that, “thankfully,” the forces opposing desegregation in the 1960s are not at work today.

Her apparent shifts prompted Democratic strategist David Axelrod to tweet that Harris’s position, supporting voluntary but not mandatory busing in most cases, seemed to resemble Biden’s: “So what was that whole thing at the debate all about?”

Harris’s struggles on the question of busing also fit a criticism that emerged in the first months of her campaign, when some Democrats said she had trouble providing a clear vision of what she stood for.

After high-profile moments, she has sometimes had to clarify her positions, including her stance on whether private health insurance should be eliminated. When reporters asked in Iowa whether she was worried about a reputation for backtracking, Harris said that she had been “consistent” on the issues.

But most voters who attended Harris’s events did not raise those concerns. And though the Iowa trip did not make life easy on Harris — who encountered sweltering heat that caused an older woman to faint at a house party, as well as rain-induced schedule changes — some of the problems were encouraging. The church that her campaign had booked to host her town hall meeting Friday in Sioux City — an arrangement made before her debate performance — was supposed to hold about 150 people.

Instead, the event drew 300, leaving an overflow crowd on the lawn to listen to Harris’s revamped message over portable speakers.