Asking for a prior restraint doesn't equal a prior restraint unless it is granted and enforced by the government. You used a legal term "prior restraint" that has a legal definition. The case you cite does not meet that legal definition.
Now if you want to argue that you are using the term "prior restraint" in a non-legal contest in which the threat of after-publication legal action and the response to that threat of after-publication legal action resulted in what is "essentially a prior restraint," then OK.
But the case you cite doesn't meet the legal definition of a prior restraint.
Yes, I used a legal term because that is what the Congresscritter was asking for, prior restraint on speech. The fact that he lost the election, and dropped the complaint, does not change the fact that he tried to use the government to stop people from placing an ad he did not like.
Now, if you want to argue that the fact that he succeeded in stopping the speech through another avenue somehow negates the fact that he actually asked the government to prevent them from running the ad, feel free. I doubt even you can wrap your head the logical contradiction that would be required t argue that way, but feel free to give it a shot.