Bill Kristol says flatly that if Mike Huckabee does as well in December as he did in November, he will win the Republican nomination for president. Two polls have Huckabee holding the lead in Iowa over Mitt Romney, and one national tracking poll now has him tied for the lead with a sinking Rudy Giuliani. What is going on here? How could this have happened?

Simple: Don’t think of Mike Huckabee as Mike Huckabee. Think of Mike Huckabee as Fred Thompson. Huckabee is filling the role Fred Thompson entered the race in September to fill. He is the socially conservative Southern pro-life candidate with a silver tongue and a pleasingly low-key affect. It was Fred Thompson who was supposed to overtake Mitt Romney in Iowa, and it was Fred Thompson who was supposed to be a force to reckon with in national polls in December. But as a candidate, Thompson has proved to have all the spark of a wet firecracker, and as John McIntyre points out,  “What we have developing is Huckabee stepping in and filling the void in the GOP field that was available to Thompson in the summer.”  Somebody was going to occupy that Thompson space.

The question was whether one of the three top-tier candidates — Giuliani, Romney, or McCain — would manage to convince that portion of the Republican base to make common cause with him. The answer, it seems, is no.

I said two weeks ago that the Republican race was down to two men, Giuliani and Romney. I still believe that is the case, because while Huckabee’s surge has given voice to an important segmentof the GOP’s electoral pie —  pro-life evangelical Christians primarily — his candidacy does not offer much, if anything, to any mainstream Republican voter who is not part of that segment. Huckabee has a record of supporting tax increases, and his major domestic policy plank is his advocacy of a wild notion called the “Fair Tax” that would replace all imposts with a national sales tax. He has little of moment to say about the war on terror, the war in Iraq, or the war against Islamic totalitarianism.

If the Republican party is still a party of policy, then Huckabee stands somewhat apart (with the exception of his stand on abortion) from the policies that have been supported by the vast majority of GOP voters and that polling tells us still unite Republicans today. Let’s say Huckabee manages to take a substantial swath of the Religious Right vote for himself — 60 percent or so. That will still leavae 75 to 80 percent of Republican voters in play — especially since there is that huge 21-state primary on February 5 dominated by the Northeast and West, which are dominated by more secular GOP voters. In a two-man showdown between Giuliani and Romney for those voters, the victor will get enough support to secure the nomination.

I can, however, see one other scenario. Say Giuliani melts down this month, owing to more revelations about the intersection of his private life and his public duties. Or Romney melts down, in part because Huckabee’s rise means he will lose Iowa and therefore make it impossible for him to win every early state and thereby “slingshot” his way into the nomination. Huckabee won’t be there to pick up the pieces, because he speaks to a different electorate.

But John McCain will….