Vice President JD Vance took his anti-fraud efforts to Wisconsin on Wednesday, raising the specter of widespread waste and highlighting an investigation that began during the Biden presidency as proof that the Trump administration was working to root out abuse.

Even as Mr. Vance portrayed the initiatives as successful and substantive policy, he also used them as a partisan cudgel. Highlighting examples of fraud committed over the course of several years — and accusing Democrats turning a blind eye to it — has become a primary political strategy for Mr. Vance and a slate of Republican candidates as the midterm elections draw nearer.

“We’ve got a party that is fighting for fraud and a party that is fighting against fraud,” Mr. Vance told a crowd of several dozen people who had assembled in an airport hangar on a National Guard base to see him. He added: “This is not about better or worse policy. This is about who is supporting fraudsters and who is supporting you.”

As Mr. Vance arrived in Wisconsin, oil prices jumped amid renewed fighting between the United States and Iran, opening a volatile new chapter in a war that has strained American consumers who elected President Trump to bring economic relief.

Instead of promoting economic policies, Mr. Vance, along with several Republicans including Representative Tom Tiffany, who is running for governor, and Representative Derrick Van Orden, who is running for re-election in a purple district he narrowly won in 2024, focused on castigating Democrats.

“We need the other side to stop turning a blind eye to this fraud that’s going on in Wisconsin,” Mr. Tiffany said, criticizing efforts by the state’s Democratic governor, Tony Evers, to keep the personal data of food-stamp recipients out of the hands of the federal government.

The Trump administration and Republicans have alleged, often without evidence, widespread fraud in various social programs after a fraud scandal in Minnesota bilked potentially hundreds of millions of dollars from state programs meant to help the poor and vulnerable. Since then, administration officials have highlighted a series of fraud charges and convictions around the country, but have also used it to try to halt funding for programs in some Democratic-led states.

Midway through his 37-minute appearance, Mr. Vance held up a large poster of Markita Barnes, a woman in Wisconsin who was convicted in March on 10 counts of health care fraud for stealing $2.3 million from a Medicaid benefit program meant to help at-risk pregnant women and women with young children. Ms. Barnes was initially indicted in 2023, during the Biden administration, but in his remarks, Mr. Vance accused Democrats of defending her.

Mr. Vance also spoke about recent efforts by the administration to roll back access to the H-1B visa program, saying it had been used to cut into wages of American workers. He told the crowd that the Labor Department had issued subpoenas to “foreign fraudsters” who may be taking advantage of the program. The department’s Office of Inspector General said on Wednesday that it had “uncovered widespread schemes” in which employers submitted fraudulent applications.

The investigation is the administration’s latest attempt to crack down on the program. Over the past year, the administration has tried to overhaul the program by attaching a $100,000 fee to new H-1B visas and pushing the allocation of the visas to higher-paid jobs. The changes have locked some employers out of the program and transformed who benefits from the program.

The program has long drawn criticism and prompted anger over instances of employers abusing the program to hire foreign workers at lower pay. Still, economists generally agree that H-1B visa holders boost American productivity and raise wages even for American workers.

There have been high-profile instances of employers falsifying applications to obtain H-1B visas over the years. The Biden administration also took steps aimed at reducing fraud in the H-1B visa program.

But there have been scant government reports thoroughly documenting the extent of fraud in the program, said Sarah Pierce, a former U.S. Citizenship and Immigration Services who is the director of social policy at Third Way, a center-left group.

Ms. Pierce said fraudsters should be pursued, but she questioned whether the investigation would become “yet another way for the administration to arrest, detain and deport more people.”

After landing in Milwaukee on Wednesday morning, Mr. Vance spent about 90 minutes at a Republican National Committee fund-raiser at the Pfister Hotel before traveling to the base to deliver his remarks. Representatives of the conservative group Turning Point USA had traveled onto the base before the event to set up a booth to register voters.

After his remarks, Mr. Vance fielded questions from local reporters. One said she had investigated fraud against prenatal programs years ago. He did not directly answer her question about what the administration would do to make sure people who needed those services would still receive help. Mr. Vance said the way to protect those programs would be to continue rooting out fraud — “money doesn’t grow on trees,” he said.

Mr. Vance was also asked about an invitation from Cavalier Johnson, Milwaukee’s Democratic mayor, to meet. In a letter to the vice president ahead of his visit, Mr. Johnson said he was alarmed that federal officials were interviewing local election workers as part of an investigation into the 2020 election results and invited Mr. Vance to see the election operation for himself.

“I will not speculate about the motives for these falsehoods other than to say it appears to be an intentional strategy to damage a fundamental pillar of our government,” Mr. Johnson wrote.

Mr. Vance dismissed Mr. Johnson’s outreach. He said the letter sent by the mayor — whom he referred to as “some guy” — seemed suspicious, and told the crowd that it felt to him like an admission of guilt similar to when his son stole cookies at home.

“It makes me wonder, why is that guy protesting so aggressively?” he said.

The crowd applauded.

Madeleine Ngo contributed reporting.