Bringing up concerns, bad decisions, potential issues, and such of a rival candidate is a valid campaign issue. We need to know the down side of our choices, not hear just the happy tidbits - that's a sure route to despotism. The issue is not negative campaigning to me, it's limiting such to realistic and respectful levels. As to why that is, I think it's the tendency of the modern mind not to react strongly to anything but the truly dramatic (and I don't limit this to America...I've seen enough other countries have their own little fits to be sure it's a human phenomenon).