OT: Political Spam - what can you do about it?

[redhat]

I have a customer on our system (we're local ISP) that fancies himself
quite the political spinmeister.  He absolutely inundates people with
his (what I call) SPAM email.  We have received numerous complaints
about this guy from all over the US (mostly colleges that he targets)
requesting that this guy be shut down.  He even "attacked" me one day
not knowing who I was and told me that he would sue us if we tried to
take his email privileges away and gave me a link to some government
site with various documents on what "is" email spam and what is "not"
email spam.  Apparently (I read all of the docs) when the lawmakers
created this anti-spam law they removed the label "spam" from anything
that is political in nature (so they could use it themselves and be
above the law).  It would appear that this guy has me beaten but I just
can't stand to sit back and watch this guy annoy other domains the way
that he does.  Does anyone else out there have any "knowledge" or
insight on this issue or can give me a link to some good resources? I
have already scoured the ".gov" sites and it doesn't look good.
thanks,
Doug