Dems, Independents, Republicans, I and my opponent all believe reducing unemployment. 

So I attack my opponent in a speech for not believing in reducing unemployment.

The result is that my Dems, Indpendents, and Republicans believe less strongly in reducing unemployment.  My opponent's rep is somewhat affected, too -- he is perceived as believing less strongly in reducing unemployment, but not enough to make this strategy workable.

This seems just plain wrong -- attacking my opponent for not being sincere about reducing unemployment is NOT likely to cause an across the board move to thinking unemployment should not be brought down!

(I have higher higher credibility and much higher charisma than my opponent, and this was in a very friendly state.)

I only wish the game had it right about real life.  If this were true, negative campaigning would not be so effective.