I've heard this argument from several people I've discussed the anthrax issue with. I always ask them how they explain the New York Post being targeted, which is about as liberal as Rush Limbaugh.
They never manage to come up with a good answer for that one.
For what are Daschle and-or Leahy famous, or notorious?
Figure out that one, and ... just maybe ... the anwser to "Why the Post?" will fall out. Maybe.
If this guess is right, it must concern something from before the WWW. All connexions recent enough to be on the Web have been scoured exhaustively by amateur sleuthers.