As a number cruncher, Romney surely recognizes that Ryan knows federal budget policy about as well as anyone. And the sometimes politically tone-deaf Romney must admire Ryan's ability, honed in hundreds of town meetings in his marginal congressional district, to explain his stances in a way that wins over ordinary voters.
Naturally, Democrats have attacked the Ryan plan as gutting Medicare and have produced an ad showing Ryan shoving a wheelchair-bound granny down a hill. They're licking their chops at the prospect of running a Mediscare campaign against the Romney-Ryan ticket.
But it's not clear that the Mediscare tactic will work when the issue gains great visibility, as it will from Ryan's selection.
For Ryan and Romney can make the point -- lost in the shuffle when this is a low-visibility issue -- that their plan would leave the current Medicare system in place for current recipients and those who are 55 or older. Those who have made plans based on the present program could continue to rely on it.
But they also can make the point that their reforms are necessary in order to make sure Medicare is sustainable in the long run. Polls show that many voters younger than 55 doubt that they ever will get the Medicare and Social Security benefits they've been promised.
One more thing about Ryan, I think, appealed to Romney. He already has shown he cannot be intimidated by the most eminent opponent. Watch the video of Ryan's five-minute evisceration of Obamacare at the president's Blair House meeting. You can tell that Obama didn't like it one bit.
He'd better get used to it. Obama's side is relying on trash-talking ads. Romney's selection of Ryan shows he wants a debate on whether America should follow Obama on the road to a European-style welfare state.