There is NO way he wins. The evangelical crowd are influential in the GOP, but they're still a small minority.
The evangelical crowd is a small minority of
all voters, but they are a significant part of the GOP. Exit polls in 2012 showed 19% of all voters were White Born Again AND voted for Romney, compare that to 32% of self-identified Republicans and you actually have 2/3s of Republican voters being White Evangelical. If you drill down more to Protestants who attend church weekly and/or those who think abortion should be illegal in ALL cases (including Rape) then you get to maybe 1/3 of GOP voters, which is still a significant portion. Remember Huckabee won IA with 34% of the vote in 2008.
Huckabee would stand a reasonable chance of winning assuming that Perry and/or Cruz is not able to cut too much into his base in the same way that Thompson did back in 04 (which probably cost him from winning SC, which was the turning point for McCain)