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NEW ORLEANS, La. -- President Obama, speaking Friday by satellite feed just minutes before a speech by GOP vice presidential nominee Paul Ryan, took a pre-emptive shot at the AARP's "Life@50+" convention, telling the group not to believe the criticisms that would follow.

“Contrary to what you’ve heard and what you may hear from subsequent speakers, Obamacare actually strengthened Medicare,” Obama said.

The Romney-Ryan camp claims the president’s health care law raids Medicare of billions of dollars, and it has made that assertion a central theme of its campaign.

Speaking to the group, which counts among its membership more than 37 million people over the age of 50, the president tried to discredit that argument.

“When you hear this notion ... that we somehow took $716 billion, robbed it from Medicare beneficiaries and seniors, I want you to know that is simply not true,” he said. "What we did was we went after waste and fraud, and over-charging by insurance companies, for example. Those savings do come out to $716 billion,”

Moments later, Ryan tried going on the offensive -- warning the crowd of what he claims will be catastrophic consequences to Medicare if voters stick with Obama.

His message was not well received.

"The first step to a stronger Medicare is to repeal Obamacare, because it represents the worst of both worlds. It weakens Medicare for today’s seniors and puts it at risk for the next generation," Ryan said to a chorus of boos.

Ryan pressed forward using numbers to support his case.

"You don’t have to take my word for it," Ryan insisted. "Ask the chief actuary at the Centers for Medicare and Medicaid Services. He works for the Obama administration, and his job is to look after your Medicare. Last year, we invited him to Congress to answer a simple question: If President Obama’s Medicare cuts were used to pay for new spending in Obamacare, how can they also improve Medicare’s solvency? His answer? They can’t."

Spatters of heckling continued throughout the speech. Ryan was cheered when he mentioned his 78-year-old mother, Betty, who is on Medicare and was in the audience.

The cold reception wasn't much of a surprise. The AARP endorsed Obamacare.

An aide to the Wisconsin congressman told Fox News after Ryan's speech that it was like entering the lion's den, adding, "it was the same reaction President Obama would have received addressing the NRA."

Ryan argues the best way to reform Medicare is to make no changes to the program for Americans 55 and older, and provide a choice of Medicare or private insurance for other future retirees.