It wouldn't necessarily take a hacker to do it.
Here is a plausible scenario: Perhaps the original MD4Bush was not the same MD4Bush from a few days ago - but the second MD4Bush used the same computer, surfed to FreeRepublic, found that the original MD4Bush account was already logged on and contained his old email.
It could be that simple - but it would be a violation of the ECPA because MD4Bush #2 was not a party to the original communication.
There are other questions (perhaps already answered?) - how did MD4Bush obtain NCPAC's identity?
NCPAC dropped sufficient hints in this forum that anyone who really wanted to could have figured out his identity. He made some posts identifying him as close to Governor Ehrlich, and his screen name would allow any reporter with half a brain to narrow down the list of who he was.
Loose lips sink ships.