For his part, Romney, in hastily arranged remarks to reporters near Boston, kept the focus on the sluggish economic recovery under Obama's watch. He cited new government figures showing that the number of American seeking unemployment benefits rose by 34,000 last week, a figure that may have been skewed higher by seasonal factors.
Both candidates were pouring most of their money and attention into the collection of fewer than 10 states expected to decide the election. Michelle Obama launched a new effort to rally supporters behind her husband, trying to light a fire by saying the whole race could "come down to just a few votes per precinct in key states."
Nowhere is the campaign potentially more pivotal than in Florida, which decided the 2000 election and remains the ultimate swing state. With a large pool of retired voters, Medicare has been used by both parties to rally support from seniors in Florida and elsewhere, mostly by warning that the other party had in mind changes that would curb the national insurance program for older Americans.
Obama sought to broaden his attack on Romney's support for a House Republican plan that would shift Medicare from a fee-for-service program into one where future retirees buy insurance using subsidies. Republicans say it would introduce competition and give seniors more choices, but it is closely watched in Florida, where about half of the 2008 electorate was 50 or older.
"He plans to turn Medicare into a voucher program," Obama said at West Palm Beach's Century Village, home to thousands of Democratic retirees from New York, New Jersey, and elsewhere. "If the voucher isn't worth what it takes to buy health insurance in the private marketplace, you're out of luck. You've got to make up the difference. You're on your own."
Romney would provide subsidies - Democrats call them vouchers - to help future retirees buy private insurance, or let them have the option of traditional Medicare, with a gradually increasing age to qualify for benefits. Current retirees would not be affected.
"[Obama] has offered no serious plan of his own to save Medicare and is content to use it as nothing more than a political issue," said Lanhee Chen, the Romney campaign's policy director.
Romney has criticized Obama's health-care law, noting that Obama calls for $500 billion in cuts to Medicare. But Obama would make most of those cuts by reducing payments to service providers such as hospitals and nursing homes, not beneficiaries.
Under the health-care law, Medicare coverage would improve for those with high prescription costs, and would require no copayments for preventive care.
During stops in Jacksonville and in West Palm Beach, Obama jumped on Romney's opposition to his health-care law, which was recently upheld by the Supreme Court. He said the former Massachusetts governor's approach would force more than 200,000 Floridians pay more for their prescription drugs.