I think blackmail can be taken as a form of threat. To use Schelling's definition (Strategy of Conflict), a threat has the property that after the person being threatened fails to perform the specified action, the threatener does not want to carry out the threat any more. In other words, the threatener has a credibility problem: he has to convince the target of the threat that he will carry it out once he desires not to. This requires some form of pre-commitment, or an iterated game, or a successful bluff, or something along those lines.
What do you see as the distinguishing difference between blackmail and a threat? (I assume that blackmail is a subset of threats, but I suppose that might not be universally agreed.)
Counterexample:
A man seduces a female movie star into a one night stand and secretly records a sex tape. He would prefer to blackmail the movie star for lots of money, but if that fails he would rather release the tape to the press for a smaller amount of money + prestige than he would just do nothing. The movie star's preference ordering is for nothing to happen, for her to pay out, then lastly for the press to find out. The optimal choice is for her to pay out, because if she pre-commits to not give in to blackmail, she will receive the worst possible outcome.
This seems to fall squarely under blackmail, yet requires no pre-committment, iteration, or bluffing.
From the last thread:
Meta: