Petraeus was definitely being blackmailed -- by his own boss "Bugsy" Obama and hatchet man "Clamps" Holder and the FBI.
When the Mob threatened to expose Petraeus if he didn't play ball, he resigned. And he'll play ball anyway, if he knows what's good for him and his family.
Another great career destroyed in a year by agreeing to take a job with the Chicago Mob. Serves him right.