This morning I introduced a formula that projects a candidate’s vote total in the Iowa caucuses based on their finish in the Ames Straw poll as well a couple of other factors. The straw poll historically does have some predictive power, particularly if you look at the share of the vote that each candidate finished with rather than simply who won and who lost.

The formula is a pretty crude tool, but it ought to be better than nothing. I’ve also made one important adjustment to it, having gone back through past newspaper accounts and taken note of which candidates “skipped” the straw poll, which I define as not have giving a speech on the day of the vote. Although candidates like these probably diminish their chances of winning Iowa by bypassing the event, the straw poll results do tend to undersell their performance somewhat.

The only other variable that has some influence on the model is the average of national polls. But the straw poll results are by far the more important factor, in accordance with what would have produced the best predictions in past election cycles.

Representative Michele Bachmann, having narrowly won the straw poll, has to be considered the favorite to win Iowa next year. The caution is that the straw poll victory comes on the heels of what hadn’t been a great month for Mrs. Bachmann. Her campaign was clumsy in batting down a variety of low-level controversies, and her standing in national polls eroded some. More important is the question of how well an Iowa win might translate into other states; it doesn’t help Mrs. Bachmann that unfavorable views of the Tea Party are increasing after the debt ceiling controversy, even among some Republican voters. But she has cleared her first hurdle with aplomb.

Representative Ron Paul came quite close to beating Mrs. Bachmann, but faces a different sort of problem. I don’t doubt that Mr. Paul could secure 15 or 20 or perhaps 25 percent of the vote in Iowa. (He got 10 percent there in 2008.) But I wonder how much upside his candidacy has beyond his very dedicated core set of supporters. The lowest-ever winning total in Iowa is 26 percent, by Bob Dole in 1988.

Gov. Rick Perry of Texas, who announced his candidacy today in South Carolina, ranks third according to the formula, which likes the fact that he won quite a few write-in votes despite not having visited Ames. Southern candidates historically have a good track record in the Iowa caucuses, which often turns out as high a percentage of evangelical voters as many southern primaries.

If Mr. Perry were to dedicate himself to Iowa, he’d have a considerable chance of winning — probably better than Mr. Paul, although not necessarily Mrs. Bachmann. The risk is that there’s no real substitute in Iowa for having had your boots on the ground, so this is the one state where his late start could be a problem. Mr. Perry’s best early states should be South Carolina and perhaps Florida. Is the best way to ensure that you’re in reasonably good shape heading into those states simply to do as well as possible in Iowa? Or, instead, to convince the media that a solid second- or third-place performance still qualifies as a “good” finish? I’d lean toward the former strategy, particularly given that if you don’t win Iowa, someone else will, and will get the momentum associated with it. But it’s a tough call.

Mitt Romney is perhaps no better than the fourth-most-likely candidate to actually win Iowa. But if he’s unlikely to win the battle, he’s made progress toward winning the war. With Mr. Perry and Mrs. Bachmann now his leading rivals, the Republican playing field is tilted heavily toward conservative candidates. That gives him plenty of breathing room, especially in New Hampshire, which will play to neither of their strengths.

This was a poor showing for Tim Pawlenty — not so much his third-place finish in the straw poll as the distance separating him from Mrs. Bachmann and Mr. Paul. Mr. Pawlenty got 14 percent of the straw poll vote. The lowest straw-poll share that any Republican winner of Iowa had was 18 percent — and that was Mike Huckabee in 2007, who faced vastly lower expectations than Mr. Pawlenty. Fundamentally, Mr. Pawlenty is in something of a catch-22: he’s an acceptable choice to a large part of the Republican electorate and would tend to do better as the field was winnowed down. But without a couple of wins in the early going, you’re going to be one of the victims of that process. Mr. Pawlenty, despite considerable efforts, has simply not convinced very many Republicans that he should be their first choice.

As for the rest of the field, this is probably not a good enough showing for Rick Santorum or Herman Cain to make them viable, particularly given that Republicans have a lot of other conservative and Tea Party-backed candidates to pick from.

Sarah Palin, who yesterday seemed to lament Mr. Perry’s entry in the race, has more upside but fundamentally the same problem should she decide to run. She would much rather have seen Mr. Pawlenty win the straw poll, in which case there would be more room on the right of the field.

You can argue, on the other hand, that Jon Huntsman should like these results. He’s still an extreme long shot since he’s a moderate running for the nomination of a conservative party. (This isn’t rocket science, folks.) But perhaps now there’s the ricochet where something bad happens to Mr. Romney’s campaign, and Mr. Huntsman rather than Mr. Pawlenty is left to pick up the scraps. Still, the upside case for Mr. Huntsman is probably winning New Hampshire and a couple other moderate states, as John McCain did in 2000 — and then getting a nice speaking slot at Mr. Perry’s convention.

Finally, there’s Newt Gingrich, a conservative running in a conservative state where he’s spent quite a bit of time — and who wound up with just 2 percent of the straw poll vote. He beat the pants off of Representative Thaddeus McCotter, at least. But it’s not clear what either of them is hoping to accomplish.