President Obama resumed his attack Sunday on the Romney-Ryan plan to save Medicare, this time referring to a study that he said shows skyrocketing costs for future recipients and further distancing himself from the dismal unemployment report released last week.

The attack marks the second straight day that the president has gone after the GOP plan, after the August unemployment report released Friday showed the U.S. unemployment rate dropped but only because more Americans quit their job search.

“Your costs would rise by the thousands and the insurance companies' profits would rise by the billions,” Obama told roughly 3,000 people Sunday at a rally at the Florida Institute of Technology, in Melbourne, Fla.

Obama also said the plan by GOP presidential nominee Mitt Romney and running mate Rep. Paul Ryan would increase insurance profits by $16 billion to $20 billion and that he would not follow their plan to turn Medicare into a voucher system.

Though the president did not specifically cite his source, senior campaign officials said the numbers come from a study by Harvard professor David Cutler.

The president picks up where he left off Saturday in St. Petersburg, focusing on Medicare and making no mention of the Bureau of Labor Statistics on Friday that showed the national unemployment rate in August dropped from 8.3 percent to 8.1 percent.

Cutler is a Harvard professor and health policy expert who served in the Clinton administration and was Obama's top health care adviser during the 2008 presidential campaign. He conducted the study for the liberal Center for American Progress Action Fund.

The Romney campaign called Cutler an “ObamaCare drafter” and said the president’s attack this weekend is “a sign of desperation.”

“Only one candidate in this race has robbed today’s Medicare of $716 billion to pay for ObamaCare – Barack Obama,” said campaign spokesman Ryan Williams. “He has done nothing to reform Medicare for the long haul and prevent it from going bankrupt. The president’s decision to use discredited studies and outright falsehoods to attack Mitt Romney is an admission that he can’t talk about his record of crushing the middle class and failing to turn the economy around.”

Romney wants to contain Medicare costs by giving retirees voucher-like government payments that they could use to either buy regular Medicare or private health insurance. But Cutler says older Americans would have to pay more out of pocket to cover the rising costs of health care.

Obama aides believe they have forced Romney to temporarily drop his emphasis on the sluggish economy last month by raising the Medicare issue in the wake of Romney's selection of Ryan as his running mate.

Romney and Ryan have countered by arguing that Obama planned to cut hundreds of billions of dollars in Medicare spending over 10 years to pay for his health care plan.

Whether either side gained politically from that debate is unclear. But Republican analysts say it did take Romney off his economic focus, which they say is essential for him to win the election, especially after a bleak jobs report that showed meager job growth and more unemployed people choosing not to seek work.

Vice President Joe Biden, campaigning Saturday in Ohio, called the GOP plan "Vouchercare."

Biden said the Romney and Ryan plan would force "Mom" to go out into the insurance market and look for the best deal she can find. If the plan costs more than the voucher amount, "They say, `Mom go borrow somewhere'" to pay for it, Biden said.

Much of Cutler's data is drawn from studies by the independent Congressional Budget Office, which has projected even higher costs to future retirees under a 2011 budget plan written by Ryan, chairman of the House Budget Committee.

The budget agency said future retirees would pay more under Ryan's plan than if they went into traditional Medicare. By 2030, a typical 65-year-old would be paying two-thirds of his or her health costs, the agency said.

Romney and Ryan are off the campaign trail Sunday, but both taped appearances for Sunday talk shows.

The Associated Press contributed to this report.