Rudy Giuliani's campaign is in *very big* trouble. It's not really because of the recent allegations that he abused spending in New York City to cover his mistress' (now wife's) security during his affair. It is because he's simply not the kind of candidate Republicans can back very enthusiastically.
Giuliani has a personally very checkered past, he's pro-choice, and he's kind of squirrely in the personality department. Reagan represented the "ideal" candidate for the Republican set of sensibilities. Handsome and imposing but also jovial and "old boy network", no-nonsense with his conservative policies, somewhat polished but not brilliant.
So, who gains from this? Huckabee. It's Huckabee v Romney now, and even though I earlier suggested Romney was "in" I think Huckabee has a shot at this if he can quickly assemble a *substantial* war chest. In America you can't buy elections, as Ross Perot's bottomless money potential only got him so far. But without much campaign cash you will lose. Period.