Using a tired government cop-out reply to answer this question = not smart. That's why he quickly cut off Warren and rolled into Obamaspeak, distorting and contorting his views then saying he can't really argue with those who believe life begins at conception. Like McCain.
It's a complicated issue indeed but for one to support abortion on demand it would seem morally required to believe that human rights begin at birth. Otherwise...
By the way, who's above a president's pay grade?