“How is my possible vote in the primary for Cain a vote for Romney?”
If Cain is in distant third place and Perry and Romney are neck and neck, then Cain support MIGHT throw it to one or the other top guys.
That’s how. But that is presuming that Cain cant win. He’s now surging strong enough that it makes it a bit arguable.
By your stated standard Perry should now drop out. He is distant third in all the polls. So if the 3rd place finisher "throws it to Romney", Perry is the spoiler not Cain.