Cain's seemingly bipolar response to "the abortion issue" is very easy to understand. As a genuine Conservative, he feels that government intervention in private decisions is wrong. As a Republican nominee for office he understands the need to appear to follow the mainstream conservative Christian influenced Republican ideal of family life: that "nice" women don't get pregnant if they don't want to, and that if they do, the woman should be forced to put the fetus' needs ahead of her own.
It's not Cain who is bipolar. It's the Republican platform.
Progressives can push this into a nice bundle of cognitive dissonance by continuing to ask, Who should make decisions: you or your government? Just keep asking.