If Newt stays in it is because the old fart is on an ego trip. He stays in for the same reason someone else his age might buy a Porsche. He is 65, and a grandfather. After this, he might make money, but this is his last shot and he refuses to enter into geezerhood. He could care less about Romney or Santorum. he could care less for the country. He does not want to admit he is an annoying old geezer: he is no longer the "idea man", he is just an aging crackpot.
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He is in denial.
Next comes anger, then bargaining (begging to be a VP candidate, perhaps?)
Then depression, and finally acceptance, which in the Newtster's case may be a postmortum experience.
He screwed up bigtime trying to impeach Clinton and shutting the government down. Now, it's payback time.