Which history are you referring to? This part of history?
https://www.youtube.com/watch?v=Y_zTN4BXvYI
Actually, there is not much evidence that negative campaigning either helps or hurts.
http://www.thisnation.com/question/031.html
It seems that Trump can get media coverage of anything he says so in his case, it may actually be advantageous as petty as it may seem to many others (including yours truly).