(Bloomberg News) Florida seniors will be living a "nightmare" because Senator Bill Nelson voted for $500 billion in Medicare cuts, the anonymous voice warns in the most-aired ad in his re-election race -- a message repeated in similar spots targeting other Democrats across the country.

It's also wrong, according to a Republican health-care expert and independent analysts.

"There are no reductions in the Medicare benefits promised in law," said Gail Wilensky, who served as administrator of the Centers for Medicaid and Medicare under President George H.W. Bush and is a senior fellow at Project Hope, a health-research organization in Virginia.

The nonpartisan Concord Coalition, a budget research group, says the ads assume insurers will cut Medicare benefits to comply with President Barack Obama's 2010 Patient Protection and Affordable Care Act, which scales back payments to Medicare Advantage plans, an alternative to traditional Medicare.

The law, its constitutionality to be determined today by the U.S. Supreme Court, also slows the growth of Medicare payments to hospitals and other health providers. Seniors' benefits weren't reduced in the legislation.

That hasn't deterred Republican-aligned groups such as Crossroads Grassroots Policy Strategies and the U.S. Chamber of Commerce from the benefit-cut assertion in campaign television commercials targeting the law that have outnumbered positive ads by a 3-to-1 ratio since measure took effect, according to data provided by Kantar Media's CMAG, which tracks campaign advertising.

Critical States

CMAG data show the erroneous claim has aired in several states that will be critical to determining which party controls the White House and the U.S. Senate, including Florida, Missouri and Nevada.

Republicans and critics of the law argue that, under Obama's law, Medicare is scheduled to grow at a slower rate, reducing spending by $507 billion from 2012 to 2021.

"The facts are clear," said Rob Engstrom, the Chamber's political director, in an e-mail. "The Chamber proudly stands by its ad and will continue to educate Floridians about the dangers of the health care law."

Even so, Medicare spending will continue to grow in real dollars. The nonpartisan Congressional Budget Office projects Medicare spending will reach $887 billion in 2020, up from $499 billion in actual spending in 2009.

Voucher Plan

What's more, Republicans assume the same savings in their own budget blueprint crafted by House Budget Committee Chairman Paul Ryan, a Wisconsin Republican. The plan would convert Medicare to a voucher plan, a proposal that's drawn scorn from seniors' groups including the AARP because it would end Medicare as a defined-benefit program. While the current law plows its projected savings back into subsidies to help low-income individuals buy insurance, the Ryan plan counts the money toward debt reduction.

Representative Chris Van Hollen, a Maryland Democrat who led his party's House election efforts in 2010, called the broadcast deluge Nelson and other Democrats are facing "breathtaking in its hypocrisy."

He said it recreates a campaign strategy from 2010, when dozens of Republican House candidates ran against Democrats by denouncing Obama's health-care overhaul for its supposed Medicare benefit cuts, helping their party win control of the House.

"They're doing it again," said Illinois Representative Jan Schakowsky, an Illinois Democrat who co-chairs the Democratic Seniors Task Force in the House.

Creating Confusion

"I definitely am concerned because, at the very least, what it does is to confuse people," she said. "A counterapproach is really going to be needed."

In Missouri, an ad sponsored by Crossroads that's run 858 times says Democratic Senator Claire McCaskill voted for Medicare cuts that could slash benefits for the program's enrollees.

In Florida, the Chamber-sponsored "Nightmare" ad says 20 million people could lose their health coverage and that seniors will see $500 billion in Medicare cuts. Nelson is seeking a third term; Representative Connie Mack IV is favored to emerge as his challenger in an Aug. 14 Republican primary.

In a Crossroads-sponsored ad in North Dakota, Democratic Senate candidate Heidi Heitkamp is attacked for endorsing the health-care law after she pledged to "never vote to take away a seniors' health care."

Coverage Loss

Other advertisements use imagery to suggest seniors will lose their health-care coverage. An ad by the American Future Fund, a nonprofit founded by Iowa Republican political operatives, flashes a picture of a distraught elderly man as the narrator cites $500 billion in Medicare cuts supported by Representative Joe Donnelly of Indiana, a Democrat running for Senate.

A spot in Virginia targets Democratic Senate candidate Tim Kaine, a former governor and Democratic National Committee chairman, with the "old, discredited charge" that he supported $500 billion in Medicare cuts, according to Politifact.com, a research project based in Tampa which has labeled the Crossroads GPS-sponsored ad false.

The Montana Republican Party is sponsoring a similar ad against Attorney General Steve Bullock, a Democrat who is running for governor.

Reduction Issue

At issue is an estimated $555 billion in spending reductions in Medicare from 2011 to 2020, according to the Congressional Budget Office, achieved primarily through slower payments to hospitals and premiums paid to Medicare Advantage providers.

Republicans are assuming the payment reductions will lead insurance companies to scale back benefits above the basic Medicare package, said Wilensky, the ex-official under the first President Bush. While saying she considers it "unreasonable to think" that there wouldn't be reductions in some benefits provided to seniors, she also confirms that such cuts aren't part of the law.

Joshua Gordon, the Concord Coalition's policy director, questions using the term "benefit cut" to describe some of the changes that could occur.

"You could be a 65-year-old senior in South Florida who is healthy and getting a free gym membership and you could lose that free gym membership," he said. "We do not consider that a benefit cut."

While it's unclear whether the savings will lead to benefit cuts, the 2012 Ryan budget proposal, issued in 2011, "clearly was a cut to benefits in Medicare," Gordon said. "The initial cut with Democrats happens to providers, and the initial cut with Republicans happens to beneficiaries," he said.