re: Criticizing your opponent's policy positions isn't going negative
An illuminating definition:
Negative ads Negative advertisements that try to persuade voters to choose a candidate by making the opposing candidate look bad, by attacking either the opponent's character or record on the issues.
An illuminating critera for a study:
A race was negative if both candidates in the general election relied heavily on attack advertisements. A race was positive if both candidates largely avoided personal or issue-based attacks and, instead, focused on reasons to vote for the candidates.