In a few months the Democrats will have their first primaries and some people will be dropping out of the race for President as the choice narrows. One really big decision that the nominee has to make is who to pick for a running mate as VP. How big of a deal to you is this really and would it impact your choice of who to vote for?
One example I think of is when McCain picked Sarah Palin and everything seemed to think "Sarah who?" It seemed to hurt his chances of winning
I have never decided if the pick of Governor Palin was a help or a hindrance. She fit the needed profile--younger than McCain, a woman, a more reliable conservative, and more dynamic. The Democrats then unleashed their usual savage (and in this case misogynous) attacks upon her, with the help of Saturday Night Live and the media.
In the end, she seemed a bad choice, but was that her fault? Probably not. She fired up a somewhat divided and pessimistic Republican base. Had he chosen someone else, the treatment probably would have been similar. Just look at the case of Dan Quayle who before nomination was a well-regarded Senator.
But getting back to your question, sometimes the choice of VP doesn't make much difference. But sometimes it does.
I used to think that it rarely did matter, but there have been some instances in our lifetimes when it really helped. Biden, for being a known commodity and an established member of the Washington set, seems to have helped the outsider and relatively unknown Obama.
Yet Bob Dole, who needed Conservative support, chose the conservative favorite, Jack Kemp, who mainly talked like an economics professor throughout the campaign and seemed determined to do as little as possible to help the man who had bested him in the race to be the GOP nominee. That was reminiscent of Henry Cabot Lodge who was chosen by Nixon the first time around as a ticket-balancer, but because Lodge didn't care for Nixon, he did little to help. If there is a lesson to be learned in those selections, it might be that someone who tried for the nomination and didn't get it isn't necessarily going to go all out for whoever beat him, even for the chance to be VP.