Now, Republicans are seeking a new winning formula for an election less than three months away. Republican pollster Whit Ayres, who has advised Senate candidates including Marco Rubio of Florida, said the party is pausing to reframe the ads by tying Obamacare to the economy and jobs, the top concerns for most Americans.

"Obamacare will not be the most important issue," and Republicans will have to "target people very directly" with their messages, said Ayres, who co-wrote a memo this month for outside spending groups such as Crossroads GPS and the American Action Network. The memo came after Ayres tested 57 possible avenues of attack.

New round

Ayres said another round of Obamacare ads may drop next month when premium increases take effect after state regulators finish negotiating with insurers on 2015 rates, he said.

"Obamacare remains of serious concern," his memo said, "garnering significant opposition among Republicans and widespread criticism among independents, who are suspicious of the law's Washington-driven approach."

Still, the party's experience across the country shows that Republicans can't count on the issue to motivate independent voters they need to oust Democrats in Arkansas, Louisiana and Alaska. And in North Carolina, the ads being run against Senator Kay Hagan also underline the limits of Obamacare as an issue.

Republicans have accused Hagan of casting the deciding vote on the law, when it passed in 2010 and became President Barack Obama's biggest legislative initiative. Yet even with more than $4 million in negative ads aimed at the law this year, Hagan is in a statistical tie with her Republican challenger, Thom Tillis, in recent polls.

Numbers reversed In April, anti-Obamacare advertising dwarfed all other spots in North Carolina. It accounted for 3,061, or 54 percent, of the 5,704 top five issue ads in North Carolina, according to Kantar Media's Campaign Media Analysis Group. By July, the numbers had reversed, with anti-Obamacare ads accounting for 971, or 27 percent, of the top issue ads, and the budget, government spending, jobs and unemployment accounting for 2,608, or 72 percent, of such ads, CMAG data show.

"It is a recognition that there's more going on in this state and also nationally than just frustration over Obamacare," said Jordan Shaw, Tillis's campaign manager. "We have never had an approach to make this campaign all about the Affordable Care Act. You can't have a conversation about Obamacare without talking about its impact on the economy."

Suing Obama

In another reflection of the party's efforts to put its campaign against the health law in a broader context, the House voted last month to sue Obama over its implementation. House Republicans said the president exceeded his constitutional powers in delaying one of the measure's central requirements on his own, without a vote of Congress.

The situation is much the same in Arkansas, where Mark Pryor is trying to keep his Senate seat, and Louisiana, where Mary Landrieu is in a tight race for a fourth term. Obamacare was just about the only issue on the air in Louisiana in April, according to CMAG. By July, it had dropped to 41 percent of the top five issue ads, and in Arkansas just 23 percent.

The ads have diminished as Obamacare coverage has expanded in North Carolina. About 581,000 people in the state had signed up for private plans under the law by April, 54 percent of the potential market, according to the Kaiser Family Foundation, a nonprofit research group.

Exceeded enrollment

Nationwide, Obamacare has exceeded enrollment projections since March as its troubled website has been fixed. Premiums in the insurance marketplaces are expected to increase only modestly in most states, and the percentage of uninsured Americans has dropped significantly, said Drew Altman, president of the Kaiser Family Foundation.

"When they righted the ship, it no longer was as effective a weapon to use to hit Democrats over the head with," he said.

Rose Duke, a 44-year-old from Raleigh who cast her ballot for Republican Mitt Romney in the 2012 presidential election, is one of Obamacare's new beneficiaries. Duke, who lost her flooring business after her husband died last year, says she now has a favorable view of the law and is angry at her state's Republican governor, Pat McCrory, for refusing to expand Medicaid under the Affordable Care Act.

Duke has a diabetic daughter who was initially denied health-insurance coverage because of the state's swollen Medicaid rolls.

"My child got caught up in the political B.S.," she said. "I had to walk in there and beg them for help," said Duke, who eventually got coverage from Medicaid, the federal-state program for lower-income Americans.

Public indifference

The dialing down of the Obamacare offensive coincides with the public's relative lack of attention to the issue.

Just 5 percent of Americans identified health care as the most important problem facing the U.S., after the economy and jobs at 22 percent and immigration at 13 percent, in a July 29- Aug. 4 CBS News poll. In November 2010 — at the last midterm election — a CBS survey ranked health care as the second-most important issue, at 17 percent, after unemployment and jobs.

The ad that has run the most in North Carolina, sponsored by Americans for Prosperity, an outside spending group founded by the billionaire Koch Brothers, proclaims that millions of Americans have lost insurance, can't see their own doctors and are "paying more and getting less."

Another features a self-employed Chapel Hill woman named Sheila Salter who says her policy was canceled and that she'll be paying $4,500 a year more for insurance.

Republican challenge

The challenge for Republicans is there may not be enough people losing coverage who can relate to the broadcast messages, to move the public-opinion needle.

According to a Gallup survey this month, the rate of uninsured people has dropped in all except five states. Two critical states, Arkansas and Kentucky, had the biggest declines. In Arkansas, the rate of people without health insurance fell from 22.5 percent in 2013 to 12.4 percent in mid-2014.

Further, recent survey data show the number of people affected by canceled health-care policies was about 1.9 million nationally, less than the 4.8 million often cited in the run-up to the health program's launch last year, according to the journal Health Affairs.

According to the memo by Ayres, the Republican pollster, arguments against Obamacare that resonate most with independent voters are economic. These include the law's cost to taxpayers; concern that it discourages some employers from hiring full-time workers, and that it will lead to higher premiums and co-payments for some in the private insurance market.

The Republican messages on Obamacare and other issues have "become more diluted" now that it is the law of the land, said Elizabeth Wilner, CMAG's vice president. "There is more material to use for messaging but they're not sure which one works best."

With assistance from Alex Wayne in Washington.

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