Do you believe abortion is ‘one’ issue independent of others?
If you can step away from the emotion of this issue, yes, it is one issue. Is it independent of others? No, there are other issues that tie into it closely. Is this (and it's related issues) the only yardstick by which I decide who might best lead this country? No.
There have been, for example, pregnant women in Iraq who have been murdered by Muslim terrorists. Therefore, should I select a right-to-life candidate who's weak on terrorism, or a candidate who's strong on terrorism but has a weaker stance on right-to-life. I just don't see things as cut-and-dried as some people do and it makes decision-making harder for me. If only one issue is of concern to a person, it would seem to me that their life is much easier than mine.
I'm not trying to say the right-to-life position is right or wrong and, clearly, I could never change either side's mind on the issue. My only point is that the job of President must touch more than just one issue and, as such, I need to know more about the candidate than their stance on just that one issue.