The eggheads at Trinity College (check the URL) make sense of the race for the Evangelical Soul:

The latest CBS poll has white evangelicals choosing McCain over Obama 58 percent to 24 percent, with 15 percent undecided. If the undecided break 50-50, that would give Obama nearly one-third of the white evangelical vote--a big improvement over Kerry's performance in 2004. For him, opportunity knocks. McCain, by contrast, has got to ratchet up his evangelical outreach. By the Republican Convention he should have locked up this part of the GOP base, and as of now he hasn't.

It's possible that this poll is an outlier, given the widely-touted possibility of Obama reaching the 40% mark with Evangelicals. On the other hand, it matches up with recent Pew polling on the subject. We'll see.

What's more interesting is to do the bar-napkin calculations: Obama hopes to reach one-half of fifteen percent of about 25% of the electorate. So .50 x .15 x .25 = .01875%. That might not sound like much, but it works out to be a hair less than 3 million voters, give or take. And given that most presidential elections are won in the 3-4% range, it's a significant margin.

So you can see why both campaigns might want to chase those votes. Certainly for McCain, it's the difference between a viable campaign and a one-way ticket to BobDoleLand.

It doesn't completely answer the question of why Obama would be working so hard to get their votes, though. Given their previous voting patterns, a fifty-fifty split in the undecideds might be a bit optimistic. Something more like 75-25 is a safer bet.

As well, it makes a difference where those votes are located. If 75% of the undecided Evangelical voters live in Appalachia and the Deep South, Obama's not going to get them no matter what. If on the other hand they're clustered in Orange County, well then, going to see Rick Warren makes a whole lot more sense.

Last, you always have to ask if it might be easier to pick up an equivalent number of votes elsewhere. Say, northern Catholics?

Bottom line: the "Evangelical vote" might make the difference between a squeaker and a full-on rout. That matches with what I'm hearing through the back channels about how hard the McCain folks are pushing "The One" ad, and where. But if Obama's counting on that 2% as his margin of victory, well, he's taking quite a gamble.

For the record, I'll stick by my previous calls: Obama takes 40% of all Evangelicals, and according to my calculations above, perhaps 30% of the white Evangelicals. If he breaks 35%, he's on his way to a 300+ EV blowout, and I'll buy Amy Sullivan and Mara Vanderslice a bottle of champagne.