Without getting into the merits of the Greater Wisconsin Political Fund ad (which was criticized by both Democrats and Republicans at the time), if JB Van Hollen really believed he had grounds for a defamation lawsuit he should have pursued it. If Van Hollen didn't believe he had grounds for a defamation lawsuit and was just filing it in an attempt to give legitimacy to his counterattack ads, then he owes the public and the Greater Wisconsin Political Fund a public apology for attempting to use the courts to silence his critics, a precedent I think partisans of both parties should be uncomfortable with.
To avoid the frivolous use of defamation lawsuits in the future, last week I proposed the following reform:
I think a better reform would be to require any candidate for public office filing a law suit for defamation within 30 days of the election to post a $5000 filing fee or bond refundable only upon successful conclusion of the lawsuit. If your reputation has truly been wrongly wounded, $5000 is a small price to pay.
This would not discourage out of court settlements as the $5000 could easily be a part of that, but the amount should be enough to discourage the filing of suits merely to attempt to intimidate your political opponents.