The Affordable Care Act cuts $716 billion in Medicare payments to private insurance companies, doctors and hospitals. The cuts are designed to slow the rate of growth in Medicare spending, and they helped offset the cost of the healthcare law's coverage expansion.
Ryan's budget would keep the $716 billion in Medicare cuts while repealing the rest of the Affordable Care Act, and that has been Republicans' primary argument to date: Medicare spending needs to be cut, but Obama shouldn't have used the savings to pay for a new program.
Republicans have said the savings should have been reinvested in Medicare, hence the confusion over the precise meaning of Romney's pledge to return the money to Medicare.
The campaign confirmed Wednesday that Romney, in a break with Ryan, would repeal the Medicare cuts outright, rather than leaving them intact and redirecting the savings.