WASHINGTON (AP) — Republican Paul Ryan's blueprint for Medicare could prove as polarizing in the campaign as President Barack Obama's health care overhaul has been. Even Mitt Romney may not want to go there.

Romney's new running mate has built a strong reputation on Capitol Hill for bold ideas to restrain health care costs and federal spending overall. His centerpiece idea is to steer future retirees into private insurance plans, with a fixed payment from the government that may or may not cover as much of a retiree's costs as does the current program.

Ryan, a conservative Wisconsin congressman and chairman of the House Budget Committee, calls his idea "premium support." Democrats call it a voucher plan. In theory, Ryan's plan could work, economists say. But the devil's in the details. Lots of them, and yet to be ironed out.