Although the House GOP plan to replace Medicare with a voucher-like system got shunted aside last week, that may not be the end of the story. Embedded in both the Republican plan and in Obama's counter-proposal is the idea of putting limits on the growth of the half-trillion-dollar-a-year program — and then enforcing them.

High-level deficit negotiations resume Tuesday under the stewardship of Vice President Joe Biden, and tackling health care spending is critical to what could become the year's most important legislation.

The two sides differ sharply on how that should be done. Obama says the GOP would leave frail seniors at the mercy of profit-driven insurance companies. Republicans say the president would empower unaccountable bureaucrats to ration care.