Oh, they work alright, otherwise they wouldn't be used. I do believe that Trump's campaign may be an exception, because people are prejudiced to see him as mean and unfair, and he doesn't have the "mantle of Christianity" to hide behind.
Smart move on their part. Somebody is paying attention to how the public responds to the publicity. He can shift back to "defense" and "negative late next week, if there is a sense that is advantageous.
Another factor is that other candidates are going negative against each other, some of the messages that Trump was putting out (e.g., Cruz won dirty in Iowa, vs. Carson) are repetitive of the messages put out by Rubio, for example.
I guess that's why I support Trump as I've heard the politicians say all this before and nothing changes.