I agree with Ross when he writes:

But with his “three golds and two silvers” and his delegate lead, Romney still looks sufficiently viable that he, not Rudy, is shaping up to be the natural “stop McCain” candidate in Florida for movement conservatives who can’t stand the Arizona Senator.

As I said long ago in the pre-Michigan era (Tuesday afternoon): 

Meanwhile, if Romney manages to win [Michigan], he becomes the default anti-McCain, leaving no room for Giuliani anywhere.  Even if Romney loses, he still has money to continue competing if he wants, while Giuliani cannot draw upon such a large personal reserve.  

Because Huckabee has decided to lay off of McCain, and prior to tonight still had strong polling in a number of Feb. 5 states, Romney faces the daunting prospect of an anti-Romney pact between the two of them, effectively shutting him out of the South on Feb. 5 and then having Huckabee drop out and endorse McCain soon thereafter.  As McCain and Huckabee divide up the spoils of February 5 and work in concert to keep Romney down, Huckabee’s withdrawal and endorsement then throw his supporters and the race to McCain.  McCain-Huckabee follows?  That might be too much for the party to swallow, but that could be Huckabee’s reward for helping to break Romney. 

P.S.  Since Romney is still the delegate leader, he was always going to be the logical opponent of whichever candidate emerged victorious out of South Carolina.