We already handle the horror of rape and incest miserably in our society. The quest to improve our response to such crises should be given the attention it deserves, completely outside the discussion of abortion. Any woman who becomes pregnant as a result of rape or incest should have immediate access to a safe abortion. That is true now and should remain true, end of discussion.
Questions of medically necessary abortions are also beside the point. When an egregiously stupid politician seeks political advantage by saying ignorant things about women's health, he should lose votes because he is egregiously stupid. When he has a national audience, creating the potential for his ignorant remarks to misinform the public, it's good for experts to step in: hence the statement issued by the American College of Obstetricians and Gynecologists to clarify that there are indeed cases in which an abortion is necessary to safeguard the health of the pregnant woman. But a medically necessary abortion has nothing to do with a woman's right to terminate a pregnancy based on criteria that she determines.
Oddly enough, Paul Ryan had it almost right. As long as abortion is legal, how someone becomes pregnant is beside the point.
It is the legal status of abortion that Republicans hope to change. Every time we let them lure us into exhaustive public arguments about what the exceptions would be if abortion were illegal, we help create space in the collective consciousness for the idea that some abortions are okay, some are not, and the difference will be determined by the state. Unless they succeed in changing the law, the question of exceptions is moot. Our only response should be, "What difference does it make? Abortion is legal."