Premium support proponents argue that replacing public insurance with vouchers to purchase private (or public) coverage will harness market forces to contain costs. But the debate often ignores traditional Medicare's administrative efficiency, purchasing power and the rewards to risk selection that accompany competition among plans. We show that despite Medicare Advantage (MA) plans' success in enrolling beneficiaries, they have been unsuccessful in lowering costs. Except in 15 percent of counties, MA costs per beneficiary exceed costs for traditional Medicare. Fiscal prudence warrants limiting MA payments to 100 percent of traditional Medicare costs, while keeping payments to MA plans below traditional Medicare in the highest cost counties.