"Click his screen name at the bottom of one of his posts."
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Thanks!
When I did, I found that his SN in the URL of his home page is abbreviated:
http://www.freerepublic.com/~duncanhunterambassad/
Looks like all profile names are truncated after twenty characters. For instance, Extremely Extreme Extremist's is http://www.freerepublic.com/~extremelyextremeextr/.
I'm guessing that the system will reject attempted signups with the first twenty characters identical to an existing user's: say, Extremely Extreme Extrovert.