The House Budget Committee chairman said that when he was first added to the 2012 Republican presidential ticket, Romney was leading Obama on Medicare. He said Obama has taken the lead by peddling falsehoods about his plan.

"When I was announced we went at this issue very hard," Ryan said. "The president has put up ads literally telling his falsehoods about what our Medicare plan is. And once people understand that they've been duped about this I think that they're just not going to buy all these arguments from the president in the final analysis."

Democrats have eagerly hammered Republicans on Ryan's budget plan and its changes to Medicare, saying it effectively guts the program and replaces it with a meager voucher system. On Saturday, Vice President Biden told a crowd of voters in Florida that a vote for Romney for president was basically a vote for Medicare cuts pushed by Ryan.

"What Gov. Romney did in picking Paul RyanPaul RyanThe Hill Interview: Budget Chair Black sticks around for now Gun proposal picks up GOP support GOP lawmaker Tim Murphy to retire at end of term MORE is he has given clear definition to all those vague assertions he was making during his primary campaign," Biden said. "[And] nowhere is it more clear what they would do than in Medicare."