Quote from tomdavis:
That's not how political strategists look at it and they're pretty good at counting votes. They look at whose vote this will change in the upcoming election. In other words, they start with a baseline of which groups voted for whom last time around and then measure the shifts. That's the most accurate way to measure voter support in an upcoming election.
Here's how this one is measured:
(a) There are very few women who voted against Obama in the last election who will now vote for him in this election because of his stand on birth control; so he picks up few, if any, votes. (b) It appears that there are now millions of Catholics who voted for him in the last election who will now vote against him.
Statistically, this one works against Obama.