That's not why Cain is in trouble.
If you recall (and Buck pointed out) his numbers were diving even before the first "scandal" came out. In debates and interviews, he's whiffed too many balls that were right over the plate, and it's gotten worse recently. It's one thing to not know who the prime minister of Lower Slobbovia is, but a candidate should have a better grasp of basic international politics or at least be able to display it.
Over many weeks Newt has been showing consistent (and pretty damn good) performances in both debates and interviews on all topics. His numbers have been slowly and steadily increasing while everyone else was looking in other directions.