Over at The Plank, Chris makes a point I'm very sympathetic to: Huckabee's rise is not necessarily good news for Giuliani, or terrible news for Romney. As Chris sees it:
Much of the Huckabee-kills-Romney thinking seems to come from the idea that, because both men are targeting social conservatives, if one is gaining support, the other must be losing it. But, apart from Iowa, where Huckabee appears to be stealing support from the entire field more or less evenly, it looks as though his increasing numbers are coming largely at the expense of Giuliani, Thompson, and (outside of New Hampshire) McCain. (Who switches from Giuliani to Huckabee? Beats me. Voters are strange creatures.)
In any case, my counterintuitive thought (sure to be utterly disproven within days or hours, given the volatility of the race) is that, in the end, Huckabee may hurt Giuliani as much or more than Romney. If Huckabee takes Iowa, it doesn't look good for Romney, but I'm not sure how it looks any better for Giuliani, who will have come in a distant third to two far less well-known candidates. Even with a bloody nose, Romney probably still wins New Hampshire, where Giuliani could fall to third or even fourth behind McCain and/or a surging Huckabee. With anti-momentum like this, Giuliani is unlikely to regain his lead in Michigan or South Carolina, where he could again come in third or worse. And if, four states in, Giuliani has yet to notch a win and rarely even been the runner-up--well, let's just say that he's not likely to be holding onto that 15-point lead in Florida...
Like Chris, I don't see how Rudy wins the nomination after finishing middle-of-the-pack in the first four contests. Also like Chris, I think Romney's still likely to win New Hampshire, as long as he gets up for a respectable second (or better) in Iowa. If that happens, and McCain can finish a strong second in New Hampshire, I think we're looking at a three-man race for the nomination involving Romney, Huckabee, and a revitalized McCain. That probably means a big showdown in South Carolina, where Romney now leads, but where Huckabee will be surging if he wins Iowa. McCain has to do well in the state (first or close second), otherwise there's no money for the rest of the campaign, in which case we're down to Romney and Huckabee.
Giuliani's only hope is a strong second or better in New Hampshire, which might arrest his recent dropoff in South Carolina and keep him alive till Florida. But, given his downward trend in New Hampshire, and the inevitable shock of seeing the ostensible front-runner finish a distant third in Iowa, I don't see it happening.
Finally, to answer Chris's question about who switches from Giuliani to Huckabee: People who vote personal charisma rather than issues or ideology. Huckabee and Giuliani are both highly magnetic characters (to Republican voters, at least). Now that Huckabee's getting a crush of mostly positive attention and Giuliani's image has been tarnished by the recent Bernie Kerik/security detail/Giuliani Partners revelations, it make sense that these voters would switch from one to the other.