WASHINGTON » Progress in reducing the number of people without health insurance in the U.S. appears to be losing momentum this year even as rising premiums and dwindling choice are reviving the political blame game over President Barack Obama’s health care law.

The future of the Affordable Care Act hinges on the outcome of the presidential election, and it’s shaping up as a moment of truth for Republicans.

If Donald Trump wins and follows through on repealing “Obamacare,” Republicans will be judged on how many people are covered — or lose coverage — by the still-evolving GOP replacement plan. If Democrat Hillary Clinton wins, the single-minded Republican focus on repeal will look even more futile.

Underscoring the stakes, a national survey finds that progress reducing the number of uninsured has slowed dramatically. The Gallup-Healthways Well-Being Index shows that the uninsured rate among adults dropped by only about 1 percentage point from 2015 through this July. That’s much less than measured in each of the past two years, since the law’s big coverage expansion started in 2014.

The survey, which polls 500 people nearly every day, is seen as a bellwether. Overall, Gallup-Healthways found that the uninsured rate among adults dropped from 17.3 percent in 2013 just before the law’s coverage expansion, to 10.8 percent currently. That translates to roughly 16.1 million adults gaining coverage over the entire period.

“It’s like box office results for a movie,” said survey director Dan Witters. “It has a big opening weekend and then it slows down over time.”

Only a change in the politics of health care can shift those numbers. That could happen, for example, if Clinton wins and Republican governors and legislators in big states such as Texas and Florida accept the law’s Medicaid expansion. But in the thick of an election campaign, both sides have an interest in maintaining their fixed positions.

The blame game has a familiar narrative.

Democrats say the law would be working much better if not for GOP obstinacy. Dug-in Republicans fostered an illusion among their fervent supporters that “Obamacare” could be dispatched easily. They kept pushing for repeal even though they knew Obama would never sign such legislation. With repeal as their official dogma, Republicans left no political space for pragmatic adjustments, the kind that divided government has produced before.

Kathleen Sebelius, Obama’s first health secretary, said Republicans have put ideology before people. She cited the failure of most GOP-led states to expand Medicaid, even with the federal government footing nearly all the cost.

“It is morally offensive when we have government blocking people from life-saving health care because of politics,” Sebelius said.

Republicans say the White House and congressional Democrats designed an unworkable program and rammed it through Congress on a party-line vote using a special procedure meant for deficit-related legislation. If premiums are now jumping and major insurers are bailing out, Democrats have only their heavy-handed approach to blame, they say.

“It continues to offer a viable contrast between the two parties,” said GOP pollster Bill McInturff, who is working to re-elect Arizona Sen. John McCain. That state has become a parable for “Obamacare” critics, with the first county in the nation in which no insurer has stepped forward to offer health law coverage for next year.

Obama’s law has reduced the nation’s uninsured rate to a historic low through a combination of subsidized private insurance and expanded Medicaid for low-income people. But it’s been no panacea for the twin problems of high health care costs and barriers to access.

Six years after the law passed, about 29 million people are still uninsured, even if coverage is now a legal obligation for those who can afford it. Insurance plans provided through the health law’s markets can be stingy, prompting some liberals to call the law the “Unaffordable Care Act.”

A poll this year by the nonpartisan Kaiser Family Foundation found that consumers getting coverage through the health law’s markets were split about whether they were getting their money’s worth, a change from previous years when a majority said they were getting a good deal.

That was before the bad news for 2017. Complaining of losses from sicker-than-expected customers, insurers are raising premiums by double-digit percentages in many communities. Some major insurance companies are exiting the markets or scaling back their roles, leaving many areas with less competition.

Republican health economist Gail Wilensky says both parties bear responsibility for the problems. If Clinton manages to stave off Trump, Republicans will have no choice but to accept the health overhaul, she said.

“I know of no historical precedent to suggest a rollback of a major benefit program affecting as many millions of people,” Wilensky said.

Just having a different president — even if it’s Clinton — could shift the political dynamics, said Republican Mike Leavitt, health secretary for President George W. Bush. “A new president can change the game by being willing to negotiate on things the Obama administration was unwilling to.”