Ron Paul. Though it's disappointing news to his enthusiastic fanbase, Ron Paul has no path to the nomination and never will. Paul wins respect for his consistency, but few can imagine him as a serious contender for the presidency. He is far more frequently described as a "kook" or "nut" than as "presidential." Paul will be lucky to win a state at all, much less the nomination. Even if a catastrophe occurred, resulting in the death of the three other contenders, the Republican establishment would see to it that someone else is nominated at the convention.
Newt Gingrich. Gingrich's path to the nomination, if unlikely, had been apparent: He could secure his role as the chief Anti-Romney, win the Southern states, and hope that he could win enough neutral battleground states to offset Romney's advantage in the Northeast, West, and "blue" states. Losing Florida by 14 points was a serious setback for Gingrich. Seeing Santorum win three states last Tuesday was ruinous. Gingrich no longer has a clear path to the nomination.
It is possible that Gingrich could get ahead of Santorum again. It would require Gingrich to do very well in the next few debates (and probably require Santorum to do badly at them). Gingrich would also need to hope Romney's attack machine cuts Santorum down to size. But even if Gingrich eventually manages to wrest the Anti-Romney vote back from Santorum, it will be too late. Gingrich needs every delegate he can get, and he can't afford to spend the next few weeks splitting the Anti-Romney vote while fighting his way back on top.
Mitt Romney. Though alarming, Romney's losses in CO, MN, and MO on Tuesday do not change his basic equation. Romney's campaign is the only one (besides Paul's) that managed to get on the ballot with a full slate of delegates in every state. For the time being, he is the only candidate with the organization and money to compete for delegates everywhere in the country. The "winner-take-all" phase of the primary is heavily stacked in his favor, with many states in the Northeast and West and few in the South. As long as Romney continues to perform well in his best regions, gobble up as many delegates as he can in the South, and use his money advantage to strongly compete in the battleground states, he is the favorite to win.
Assuming Romney is able to "vet" Santorum with the kind of negative ads that destroyed Gingrich in Iowa and Florida, Santorum's resurgence will be to Romney's benefit. Obviously Romney would prefer to compete against Gingrich than Santorum. But if both of his competitors are robust without being too strong, they'll split the Anti-Romney vote. Moreover, at some point Santorum and Gingrich will need to bow to the reality that they are competing with each other for the same voters. It's tempting for Anti-Romney voters to wish for a truce between Gingrich and Santorum, but it simply makes too much sense for Gingrich and Santorum to attack each other instead. There's a reason why Gingrich was demanding that Santorum drop out of the race, and it wasn't ideological disagreement.
Rick Santorum. Despite his disadvantages, Santorum now has a clear path to the nomination. It's not an easy one, and those disadvantages (lack of money/organization, failure to fully qualify on ballots in several states, having yet to be vetted, etc.) are more likely to sink him than not. Still, he has a path. Santorum is in a race against time. He must do well enough against Gingrich in the next several contests to push him out of the way and fully capture the Anti-Romney vote before Super Tuesday. Santorum can win if he is able to dominate the South and the Midwest, while performing decently in Romney's strongholds of the Northeast and West.
The challenge for Santorum is that he must squeeze Gingrich out of the race and take all the Southern delegates for himself. The South is the most anti-Romney region, as well as being the most pro-Gingrich. In a two-man race, this would not matter: Without Gingrich in the running, Gingrich voters would happily go over to Santorum instead of Romney. In a three-man race, it's different. Santorum is faced with the task of getting pro-Gingrich voters in the South to abandon Gingrich and join him. To do that, he needs to beat Gingrich enough to make Gingrich's candidacy look like it's over, and in a hurry.
