Mike Huckabee is the first serious Christian identity-politics presidential candidate. He is not running as the only hard-line pro-lifer, though he probably is the only one. He is not running as the most conservative candidate, which, at least on the issues of taxes and foreign policy, he certainly is not. He is running, most prominently, as an evangelical Christian and structuring his appeal to those who share his beliefs. His meta-message: I am one of you. The Mormon from Massachusetts is not. The New York Catholic with the messy private life is not. The sleepy television star is not. I am your brother.

The Christian base of the Republican party is unquestionably important. It may make up as much as 35 percent of the primary vote. If Huckabee wins a landslide majority of evangelical votes nationwide, say 65 percent, he will have in his pocket one-fifth of the Republicans participating in the primaries. That’s a very significant number in a populous and divided field.

But here’s the thing: It’s not enough. The Huckabee math leaves another 80 percent of Republican voters up for grabs to choose between Giuliani, Romney, Thompson and McCain. Assume that a huge defeat in Iowa for Thompson causes him to withdraw from the race, which is a safe assumption. That leaves three candidates contending for the non-Huckabee vote. If they were to divide that vote evenly (which won’t happen, but it’s worth thinking of it this way), they would each receive 26.5 percent of the overall vote, and would do so, moreover, in populous states where there are a lot more delegates to be had.

The problem Huckabee faces as he moves into the first tier is that, aside from his very pleasing demeanor, he is not giving any other kind of Republican — a national-security Republican, a small-government Republican, a low-taxes Republican — any reason whatever to vote for him. Everyone understands you can’t win without the base. But the obsession with winning the base can blind some people to this basic fact: A man cannot win by base alone.