I haven't researched the issue in depth, but at a cursory analysis, I think the First Amendment would make any such criminal prosecution theory sink...and you would find it difficult (to say the least) to get a U.S. Attorney to even look at the case (based on a theory of obscenity and interstate trafficking in porn). We weren't able to even get the ban on kiddie internet porn to withstand the absolutists currently haunting the U.S. Supremes.
And unless the perpetrator just so happens to live in your jurisdiction, you will not be able to enlist State or County agencies...which would be even less likely to do anything. Unless you could first obtain a protective order (TRO in legal parlance) to bar the nuisance activity. Then repeated violations would give you more solid standing to go after the character.
The victims and the Corporation (Free Republic.com) would perhaps have standing to bring an civil action sounding in tort law, the tortious interference in business (restraint of trade), defamatory damaging of business reputation, and on the personal level, intentional infliction of emotional distress.
As a furst step, I suggest that the Moderators be given the ability to "nuke" all posts and email by such an obvious troll...and spare the victims the angst that you rightly express. I assume that the guy must be using an alias when he registers.
Perhaps a precondition should be made so that Free Republic posting privileges require a secure ISP-tracking cookie be enabled on the posting system.
FR isn't a money-making entity so I see the above going exactly nowhere.
Probably the key thing is to limit comments on the guy's posts to mail to admins and not starting long threads like this filled with outraged comments; this gives the guy precisely what he wants.
How about making porn available to minors??? many young FReepers come to this site.
Personally, I long for the days when kickin' the livin' shi'ite out of a piece of scum like the one in question would have folks writing congratulatory letters to editors.
Manners would be much improved.
While I don't agree with your analysis of what legal recourse action we have, I definitely agrree with a nuke option where the mods, Jiim, and/or, John Rob could destroy the poster and lall his/her posts, including pings to others.
To Mr. Jim and John, apologies I am pinging you a lot but some really great ideas are being floated around here.