In a speech in Fort Myers, Biden said that Romney's running mate, U.S. Rep. Paul Ryan of Wisconsin, is the Republican Party's "ideological center," The Hill reported.
"What Gov. Romney did in picking Paul Ryan is he has given clear definition to all those vague assertions he was making during his primary campaign," Biden said.
Ryan, in a plan to cut the federal deficit, included converting Medicare to a system in which senior citizens would receive vouchers to buy private insurance. The change would not affect anyone currently on Medicare or within 10 years of becoming eligible, Ryan has said.
Romney has been criticized for failing to provide details about changes he has proposed -- for example, saying tax cuts would be paid for by closing loopholes but not specifying which loopholes he would close.
Biden suggested the choice of Ryan filled in the gaps.
"So now we don't have to guess about what Mitt Romney means when he talks about Medicare vaguely and Social Security and education and all these things, because it's almost like two incumbents running," Biden said. "We don't have to wonder anymore, 'Exactly what does Gov. Romney mean?'"