Attack can mean any ad that describes your opponent in an unfavorable manner. I would find it very difficult for instance to truthfully describe Trump in any manner other than 'unfavorable'. Rather I would propose that we outlaw LIES in our politics. We have made it a crime to slander or libel others, because lies that cause harm to another is seen as something we as a society have determined is harmful to our society. Lies in our politics cause harm on a much larger scale, for our elected officials have the power, in fact the responsibility to make choices with will affect the lives, or even end the lives of large numbers of people in our country. If they justify these choices with lies, or simply gain the position through the use of lies, clearly there is great harm being done. The challenge would be in how to punish in a meaningful way to discourage the practice and to make the determination in both an unbiased and timely manner so as to make a difference.

There are many different flavors or political attack ads. Those that truthfully highlight differences among candidates serve a role, though I think most tend to distort, often unfairly, to achieve maximum impact.