This ad from New York Democratic Rep. Tim Bishop has the right idea: defend Bishop from Republican attacks, and then quickly pivot to hitting Republican Lee Zeldin. However, it starts off making one major mistake when it repeats those same Republican attacks.
The narrator declares, "Tim Bishop is not under FBI investigation, they found no wrongdoing." It's rarely a good idea to repeat your opponent's attack, even if you're trying to counter them. When the narrator brings up the words "Tim Bishop" and "FBI investigation," he's actually helping keep the original GOP attacks in circulation.
A similar example is Richard Nixon's famous "I'm not a crook," line. Even without knowing the context of Watergate, the people hearing it are far more likely to associate the words "Nixon" and "crook" than "Nixon" and "honest." The congressman did need to address the allegations but there were more effective ways to do it. For instance, he could have described how ethical he was, not how he wasn't unethical. Bishop ended up losing by 10 points, in large part due to questions about his honesty.