It appears to me that Mitt Romney's selection of Paul Ryan as his vice presidential running mate may have presignalled the re-election of Barack Obama. I say this because the goal of a presidential run is to win. It follows that a vice presidential candidate should be one that most helps the standard bearer achieve this end. I believe there is someone else that would have helped Romney more than Paul Ryan.
I can think of three areas where Romney is going to need a lot of help. First of all, and most important, he is going to have to split the all important Hispanic vote. Next, he will have to capture as many of the women's votes as he can. Thirdly, being a Mormon, he must woo as many Catholic votes as possible. Paul Ryan can only help him here. But the one person in the mix that could have helped him in all three categories is the governor of New Mexico, Suzanne Martinez.
You'll notice I haven't gotten into the merits of the known vice presidential candidates. After all, this is about winning an election, not judging one's credentials.