If former US presidents where prosecutable every US president since at least Nixon would have been in Jail.
The policy of prosecuting former presidents is an assurance for whoever the current is president that he he wont go to jail for whatever he does like start a war on false pretenses (e.g Iraq, etc)
It's a "feature" of the current system, not "a flaw". And it sucks.
@scubbo ok, maybe not Jimmy Carter. @rbreich