All in all, then, on a series of difficult policy questions, Ryan has either pushed his party in a politically risky but more responsible direction (on Medicare reform) or else endorsed the riskier but more responsible approach himself (on health care and Social Security reform). He has twisted arms when arm-twisting was possible and flown solo when it seemed necessary. To the extent that there is a plausible Republican response to the Obama agenda, he’s the biggest reason it exists.