Since the Bipartisan Campaign Reform Act of 2002, a candidate’s television and radio ads must include “a statement by the candidate that identifies the candidate and states that the candidate has approved the communication.” This is why almost every American campaign ad contains the sentence “I approve this message.” The rule is known as the “Stand By Your Ad” provision.
The goal was to discourage negative ads, because the candidate would have to own them personally. It did not work. Negative ads continued to grow, and some researchers found that the candidate’s statement made certain attack ads more persuasive.