Susan Page

USA TODAY

WASHINGTON — The Affordable Care Act looms as a powerful issue in this year's congressional elections, a USA TODAY/Pew Research Center Poll finds, and one that is reverberating in ways likely to boost the GOP.

In the survey, taken after President Obama announced a surprising 7.1 million Americans had signed up for health care through the law's exchanges, more than eight in 10 registered voters say a candidate's stance on the law will be an important factor in determining their vote. A 54% majority call it very important.

By 2-1, those who rate the issue as very important disapprove of the law.

That means it is more likely to motivate opponents than supporters to vote — a critical element in midterm elections when turnout often is low.

Kansas Sen. Jerry Moran, chairman of the Republicans' Senate campaign committee, says he has seen other evidence of that intensity gap. "If you don't care about Obamacare, you're less likely to vote," he said at an interview with USA TODAY's Capital Download. "If you think Obamacare is good, it's not a big issue for you. But if you think it's bad, it's an intense one."

Four years after it was signed into law — and six years after the issue helped elect Barack Obama president — the health care overhaul is poised to help define yet another election. At least at the moment, it is increasing the odds that Republicans will be able to score the net gain of six seats they need to control the U.S. Senate for the final two years of the president's tenure.

"Senate races are not a referendum on any one issue, and instead are a choice between the two people on the ballot," said Colorado Sen. Michael Bennet, chairman of the Democratic Senatorial Campaign Committee. "Up and down the map, voters will choose between a Democrat who is fighting for their states and a Republican who has embraced a reckless and irresponsible budget that's good for the special interests and bad for their states. We're very confident that when faced with that contrast, voters will side with the Democratic candidate."

Americans continue to disapprove of the law, now by 50%-37%. The share who say they don't know or won't answer has jumped, to 12% from 5% when the question was asked in February and last December.

So far, most Americans, 57%, say the law hasn't had much of an impact on them or their families. In coming years, they predict by 35%-29% that it will have a mostly negative effect on them. In a survey that has mostly bad news for proponents, that 6-percentage-point gap may provide a glimmer of good news: It has narrowed from 12 points in December.

Asked about the effect on the country as a whole so far, 43% say it has been mostly negative, 30% mostly positive. That's a bigger shift, to a 13-point gap from a 26-point gap in December. That may reflect some reassessments as the heart of the law goes into effect.

Still, the downbeat assessment of the health care law over the long term hasn't budged. By 44%-38%, those surveyed say its overall effect in coming years will be mostly negative.

The partisan divide is stark. Republicans by more than 8-1 disapprove of the law. Democrats by almost 5-1 approve of it.

In the poll, 42% identify themselves as Republicans or leaning to the GOP, 39% say they are Democrats or lean to the Democratic Party.