When candidates put attack ads on TV it diminishes their credibility.
I was living in New York for the summer when Hillary C. first ran for senator. The jamoke who ran against her was such a weakling, all he could do was attack her. He lost mightily.
I also recall a governor's race in my homestate where the Democrat female candidate had a sizeable lead, until she put out the dumbest attack ad linking her opponent to murder because he'd sponsored some business in a 3rd world country where some really bad violence took place. She blew it. The opponent won.