(CNN) -- President Barack Obama and GOP vice presidential nominee Paul Ryan on Friday traded sharp criticism over health care reforms and Medicare, with each telling a leading advocacy group for senior citizens that the other was being untruthful. "Contrary to what you've heard and what you may hear from subsequent speakers, Obamacare actually strengthened Medicare," the president told the AARP Liffe@50+ event, using the nickname for the 2010 Affordable Care Act that passed with no Republican support. In particular, he called the claim by Ryan and other Republicans that $716 billion is being cut from Medicare to fund the health care bill "simply not true."
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NEW: Sen. Reid says Romney still isn't coming clean on taxes
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Paul Ryan gets mixed reception at AARP event
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Ryan and President Obama accuse each other of being untruthful
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Obama says leadership means rejecting bad ideas
Romney
In a separate development, @placeholder released details of his 2011 income tax return that showed he made $13.7 million last year and paid $1.94 million in federal taxes, giving him an effective tax rate of 14.1%, his campaign said.
Obamacare
"The first step to a stronger Medicare is to repeal @placeholder because it represents the worst of both worlds," Ryan said to loud booing.
Paul Ryan
Ryan
Paul Ryan
Ryan
"The first step to a stronger Medicare is to repeal Obamacare because it represents the worst of both worlds," @placeholder said to loud booing.
Medicare
Medicare
Medicare
In his remarks, Obama argued that Medicare savings come from "using the purchasing power of @placeholder to say to doctors and hospitals and insurance companies: 'You guys need to work smarter."
Barack Obama
Obama
Obama
With polls showing Romney unable to overtake @placeholder with less than seven weeks to go until the November election, GOP infighting is showing a rising frustration over the candidate's campaign against a president saddled by high unemployment and a sluggish economy.
Barack Obama
Obama
Obama
New figures show @placeholder and his allies raised nearly $85 million in August, outpacing Romney's haul in the month that included both parties' national conventions.
Romney
@placeholder tweaked his campaign strategy twice this week in response to controversies that distracted from his main message challenging Obama's record as president.
Barack Obama
Obama
Obama
Romney tweaked his campaign strategy twice this week in response to controversies that distracted from his main message challenging @placeholder's record as president.
Barack Obama
Obama
Obama
The @placeholder camp fired back that the criticism was off base.
AARP Liffe@50
AARP
He noted that @placeholder supported the 2010 health care reform act and opposed Ryan's Medicare proposal.
Paul Ryan
Ryan
Paul Ryan
Ryan
He noted that AARP supported the 2010 health care reform act and opposed @placeholder's Medicare proposal.