Uwe Reinhardt, a health care economist at Princeton University, said there's no evidence the growth of health care spending will correspond with the rate of economic growth. Health care spending has slowed recently, but some expect it to jump back to higher levels when the economy improves.
"The supply side of the health system is simply not yet under control," Reinhardt said. "I believe the insurance industry is too fragmented to have the market power to control prices."(Watch Mitt Romney in St. Augustine, Fla., on Monday vow to protect Medicare)
Instead of spurring insurers to control their costs, Reinhardt said the Ryan plan would leave seniors out to drift. "You're essentially shoving these guys out on a boat, saying, 'We'll give you a push, but if the waves are rough, you're on your own," he said. "It would really worry me if I were a middle-class American."
Antos said that seniors will end up paying more out of pocket under any Medicare reform plan out there -- "the world is not getting better in that regard."
Still, he said, "In a premium support world, they're going to make up their minds" about the health care they use.
Critics of the Ryan plan also charge it could deteriorate the traditional Medicare plan by turning it into a dumping ground for less healthy seniors. Through the mechanism of "risk adjustment," the government should theoretically offer bigger vouchers for sicker consumers, but Reinhardt said risk adjustment has been the "Achilles' heel" of any competitive scheme.
Antos countered that the size of the vouchers will be overseen by the government. "The fact is that premium support health care is a government program," he said. "Ryan's plan has never said we're going to abolish the oversight... This is not going to be some kind of wild west rodeo."