By BILL BARROW and MELINDA DESLATTE, Associated Press

BATON ROUGE, La. (AP) — An old political standby — the future of Medicare — is emerging as the go-to issue in Louisiana's bitter Senate race as the candidates woo seniors who typically wield strong influence in midterm elections.

The challenge for voters is to figure out which side, if either, is telling the whole truth about who would cut and who would protect the popular insurance program. Medicare serves more than 50 million people and accounts for about 15 percent of federal spending, with about 10,000 new beneficiaries added daily as baby boomers reach age 65. The issue is so powerful that it's cropping up in North Carolina and Iowa, too, amid a national battle for control of the Senate.

Louisiana Sen. Mary Landrieu got hundreds of seniors grumbling at a recent forum when she told them her top Republican rival, Rep. Bill Cassidy, wants to turn Medicare into a "voucher system" and has voted to raise the retirement age to make Americans wait longer for benefits.

"No wonder Bill Cassidy didn't come today, because he didn't want you to know this," said Landrieu, who finds herself in another tough re-election bid as she seeks a fourth term.

Landrieu has made the issue of entitlement programs for the elderly a centerpiece of her campaign, traveling Tuesday to three senior centers across south Louisiana to announce a new endorsement from the National Committee to Preserve Social Security and Medicare, a Washington-based advocacy group.

The Senate Democrats' campaign arm has aired an ad against Cassidy featuring three older white women — a crucial demographic for Landrieu in a state that President Barack Obama twice lost badly — bemoaning Cassidy's plan that "(requires) seniors to buy private insurance with fewer benefits and higher costs." Democrats have hit Iowa Republican Senate nominee Joni Ernst with similar ads.

Cassidy and his backers answer that it's Landrieu who cut Medicare when she voted in 2010 for Obama's signature health care overhaul, which reduced payments for private policies under the Medicare Advantage program.

Americans for Prosperity, the political action organization backed by the conservative billionaire Koch brothers, Charles and David, cites that Affordable Care Act vote in similar ads opposing Landrieu and her North Carolina colleague, Sen. Kay Hagan.

The three races are among the handful that will decide which party controls the Senate for the final two years of Obama's presidency. Republicans must net six more seats for a majority.

The back-and-forth reprises a major theme of the 2012 presidential election. Obama and Republican nominee Mitt Romney leveled the same attacks, with Romney prevailing among voters older than 55. The issue also helped Republicans in 2010, when the GOP used dissatisfaction and confusion over the new health care law to win a House majority.

While Republican Medicare attacks are based on the health care law, the Democratic attacks are based mostly on House Republicans' budget blueprint, the Paul "Ryan Budget," so-named for the Wisconsin congressman and budget chairman who was Romney's running mate.

The Affordable Care Act changed how Medicare pays doctors and hospitals and included reductions — the $700 billion in cuts the GOP cites — in Medicare Advantage, which allows seniors in certain markets to purchase coverage from private insurers.

Ryan's budgets, meanwhile, propose a long-term shift to a voucher system for seniors' health care, where beneficiaries would get taxpayer money and then choose among traditional Medicare and private policies sold on the open market — similar to the exchanges the health care law set up for working-age Americans. The House has stopped short of passing legislation that would actually implement the overhauls assumed in their budget plans, and the budget votes have been largely symbolic anyway since Republicans have the political cover of a Democratic Senate, which routinely kills legislation passed in the House.

Medicare's latest annual report, issued this summer, projects that the program's hospital trust fund won't be exhausted until 2030, at which time payroll taxes are projected to cover just 85 percent of Medicare's costs. Yet each side persists in attacking the other's proposals as untenable "cuts."

"The $700 billion that Obamacare cut from Medicare spends it on other programs," Cassidy said, referring to the law shifting some health care spending to premium subsidies for working-age policy holders. "The $700 billion in the Ryan budget puts it back into the trust fund."

Landrieu and Democrats argue that the new law covers more Americans and, thus, lowers health care costs across the board by saving on treating the uninsured.

Democrats also note Congressional Budget Office projections that premiums for traditional Medicare could nearly double under the Ryan proposal, leaving seniors to choose the more expensive public insurance or less expensive private plans with lower benefits and more out-of-pocket expenses.

Analyses from the insurance industry and independent groups note that under both parties' models there would be rural areas where private firms may not offer policies at all.

Landrieu's most aggressive criticism of Republican Medicare plans, meanwhile, ignores that the changes would not affect anyone who is old enough now to qualify for Medicare. That means none of those voters Landrieu stirred up at a senior center would be forced off traditional coverage under plans Cassidy has supported.

Nonetheless, Landrieu defends her attacks. "You can only judge what somebody's going to do based on what they've already done," she said.

___

Barrow reported from Atlanta. Follow the reporters on Twitter @BillBarrowAP and @MelindaDeslatte.