Ramesh, John–President Bush has actually said pretty plainly that he thinks abortion should be illegal in all cases except rape, incest, or a threat to the life of the mother. Here he is for instance, in an interview from 2005:
I’ve always believed that there — we ought to — abortion ought to be illegal with the exception of rape, incest, or life of the mother. But, look, I’m a realist, as well. I mean, this is an issue that has polarized the American political society. And in order to get good policy in place that protects the life of a child, we’re going to have to change hearts
So if that’s a standard for Thompson, it’s a fairly clear standard.