"The American people have already rejected this plan before -- and this year will be no different," said Minority Leader Nancy Pelosi, D-Calif. "The Republican proposal would end the Medicare guarantee, shift costs to seniors, and let Medicare wither on the vine while providing billions in tax breaks for Big Oil and special interests and destroying American jobs."

Republicans say the new approach on Medicare forces competition upon a wasteful health care system, lowering cost increases and giving senior more options. But opponents say the new system -- designed by Ryan and liberal Democratic Sen. Ron Wyden of Oregon -- cuts costs too steeply and would provide the elderly with a steadily shrinking menu of options and higher out-of-pocket costs. 

Rep. Peter Roskam, R-Ill., chief deputy GOP whip, said the plan addresses a critical and looming crisis. 

"This is the most predictable event in history -- that is a debt crisis of the United States, if we don't act," Roskam told Fox News.