Governor Romney’s choice of Rep. Paul Ryan as his running mate surprised me. The safe pick would have been Senator Portman or Governor Pawlenty. Nate Silver had Portman raising Romney’s probability of victory by 1% whereas Ryan has nearly no impact (he’s not very popular in Wisconsin outside his district).
The electoral consequences of this choice are likely to be negligible. Think about the worst vice presidential choices, Dan Quayle, Sarah Palin, Geraldine Ferraro. None of them changed the result of the election. The best ones, Al Gore, Lloyd Bentsen, again no difference. Dick Cheney probably is the only veep choice in modern times that influenced an election result, but that election was so close that everything either candidate did influenced the result.
However, the Ryan pick does raise the stakes of the election. It makes the ticket undeniably more conservative and signals that Romney is continuing to run away from his record. (as Steve Benen points out, it also takes attention away from Obama’s record as a focus of the campaign) If one is concerned about the future of Social Security and Medicare, this puts them in the center of the election. My guess is that it will energize conservatives and liberals (much like the Palin pick) and turn off moderates. But at the end of the day this is still a choice between President Obama and Governor Romney.