President Obama said on Thursday that enrollment in health coverage under the Affordable Care Act had reached a new high, 20 million, and he called the law an overwhelming success in this city and around the nation despite Republicans’ implacable opposition.
“Congressional Republicans have tried and failed to repeal Obamacare about 60 times,” Mr. Obama said to an audience here. “They have told you what they would replace it with about zero times.”
He continued, his voice rising: “If they got their way, 20 million people would have their insurance taken away from them. Twenty million people!”
The 20 million figure includes people who have received private health insurance on exchanges, those who gained Medicaid coverage under state expansions and young adults who were able to stay on their parents’ health plans until age 26, the administration said.
In its last comparable estimate, in September, the administration said 17.6 million uninsured people had gained coverage.
Mr. Obama’s trip was intended to reward Milwaukee, which won a nationwide competition called Healthy Communities by enrolling an estimated 38,376 people in private health insurance under the health care law. That was about 75 percent of previously uninsured residents who were eligible, a rate higher than that of any other city.
The law has been particularly successful in places like Milwaukee, where a coalition of local leaders, charities and health care companies have worked to sign up those who did not have health insurance.
Average insurance premiums in the city fell 2.1 percent for 2016 plans, according to the Kaiser Family Foundation. “It’s an example of what community outreach can do even in the face of a governor who is not supportive of the A.C.A.,” said Drew Altman, the president and chief executive of the foundation, which focuses on health issues.
Wisconsin’s Republican governor, Scott Walker, who has disparaged the health law, expanded the state’s Medicaid program just short of the level that would allow the state to receive hundreds of millions of dollars in federal aid.
Mr. Walker has argued that federal funding is uncertain over the long term. “If anyone thinks the federal government, which is currently $18 trillion in debt, will not renege on its future funding promises, they are not living in reality,” Laurel Patrick, the governor’s press secretary, said in an email.
But no state would save more money by further expanding Medicaid than Wisconsin, according to an estimate by the Wisconsin Council on Children and Families, a nonprofit group.
“Your governor still refuses to expand Medicaid, which, by the way, actually would save money,” Mr. Obama said. “He’s denying Wisconsinites their ticket to health insurance, and it’s political.”
The Milwaukee county executive, Chris Abele, a Democrat, said in a speech on Thursday that city leaders were pleased to win the Health Communities contest, but that it was not the motivation for their efforts.
“We did it because thousands of people in this county who never had health care before do now,” Mr. Abele said. “We also did it because the Affordable Care Act has already saved — I wrote that in big, bold letters — saved the county over $2 million.”
Before Mr. Obama’s address at a middle school, he stopped at a restaurant, Engine Company 3, to speak to a handful of people who had written letters to him about the law. Among them was Brent Brown, of Mosinee, Wis., a Republican who later introduced the president to a raucous crowd of about 700 at the school.
“To be clear, I have never voted for President Obama,” he said. “Ever.”
Mr. Brown said that the health law had saved his life after he became desperately ill.
“And to the Republicans who wish to repeal the Affordable Care Act, I plead with you to reconsider,” Mr. Brown said. “Swallow your pride — as I am doing right now in front of many Democrats — and do what is right.”
Mr. Obama said that as many as 129 million Americans with pre-existing conditions could no longer be charged more or denied coverage because of that prior illness, and that 140 million Americans now got free preventive care such as mammograms.
“So your insurance is better than it was even if you don’t know it, even if you didn’t vote for me. Thanks, Obama,” the president said to a roar of laughter. “You got an upgrade.”