Mitt Romney’s decision to tap Rep. Paul Ryan (R-Wis.) as his running mate puts Medicare front and center in the presidential race. In an unusual twist, both the left and the right had been pulling for Ryan as Romney’s choice.

Congressional Democrats were already using Ryan’s controversial budget plans, which would turn Medicare into a system of private insurance partially funded by government subsidies, as the cornerstone of their attempt to take back the House.

Conservative Republicans had reservations about some of Romney’s past policy positions — especially his support for a law similar to Obama’s healthcare reform. But Ryan has the bona fides, and for a decade he’s been leading calls to cut the deficit and rein in entitlement programs.