Between Romney's corporatism and minority religion, and Newt's basic Newtery, Tea Party and evangelical enthusiasm is drying up fast.  Its already reflected in consistently low turnout. If that happens, the GOP's goose is cooked. 

And to throw a candy cane in there, the only honorable Christian in the race is going to be Barack Obama.  Why would Newt stay in?  He must know he's an amazingly weak candidate against any sitting president -and although just running while the other person has a chance of tripping is a factor- two things explain his vicious campaign behavior. 1 is obvious- his narcissistic personality disorder, which makes Palin look like "trying to think of a stereo-typically humble American and failing."

2) is more interesting and subtle: I'm calling it an attempt by a strong Christianist base - as Sullivan calls it - to save the Republican Party from Mormon domination. I strongly suspect that a lot of people in the GOP leadership would rather preserve Christian religious domination that mount an effective candidate against Obama. Why? Long term - Mormonism is a tiny and permanently insular religious minority. This isn't Catholicism - we're talking small single digit minority. If Romney fails against the President, but succeeds at leading the party, staffing it, and organizing it, I would suspect that the calculation is that the Republican movement would start losing its ability to motivate christian traditionalists of all stripes, and thereby, start moving into permanent minority mode.  The

Romney's motivation, on the other hand, is in many ways missionary.  Recall his deeply asinine speech on religion in politics from the last campaign, which, instead of calling for tolerance, called basically to unite around the common enemy of non-believers. What does he want? Power. Why does he want it?  Core religious identity - and not exactly selfish.

The casserole in the oven is:  if he takes the GOP nomination, he has permanently legitimized Mormonism.

Expect at the minimum a threat for a third party run from Paul- which would, if he sticks with it, would -guessing- take about 4% from the right and 2% from the left.  For the same reason, not to win, but to preserve that social darwinist/Libertarian influence - he will be negotiating for platform points, and would be quite happy to drop the bomb on the GOP if he's shut out.  And Romney is likely to shut him out.