One week. That's all the time left in the 2008 Iowa caucus campaign.

While many are ready for it to be over - caucus-goers are tired of the robot calls, and political and media types are tired of the same old restaurants - the race remains delightfully undecided.

That means one week from today, some real news is going to be committed in Iowa.

The big question is: "Who is going to win?" (Since I stupidly answered that question in a pre-caucus column four years ago - Howard Dean - I now quote Mark Shields, one of the most respected political columnists in our business, who told Jim Lehrer something to this effect: That is a very good question, Jim. And I would be a fool to answer it.)

So let's look at third place.

Third-place showings are likely to hold exactly opposite meanings in the two parties this cycle.

On the Democratic side, a third-place finish will severely wound a leading candidate, perhaps mortally. On the Republican side, it just might provide a shot of political steroid for a lagging candidate as the race heads to New Hampshire.

Some background: Throughout the history of the modern early caucuses, no candidate who has ever finished worse than third in a competitive race has ever gone on to win a nomination. As has been noted here before, there are three tickets out of Iowa to New Hampshire on the morning after: first class, coach and standby.

Among the Democrats, polls show that Barack Obama, John Edwards and Hillary Clinton are in a close race for first place. All need to win. Clinton's been the national front-runner and needs an Iowa victory to certify that standing. Obama has come on strong at the end, and if he defeats Clinton for first place here, he stands a chance of pulling a John Kerry: Use an Iowa victory to run the table of subsequent contests and capture the nomination.

For Clinton to finish second behind Obama would be a defeat, though she will spin it that she had a successful effort in the state because she started so far behind here.

John Edwards finished second last time and must do better than that now to survive. He's already seen as a bit of a one-trick pony who has a great campaign in Iowa and little elsewhere. It's an observation he disputes.

The only common thread to this is that third place to any of them would be a dead zone. On a plane as full as the Democratic one, there is no standby ticket out of Des Moines on Jan. 4.

Polls also show there is so much distance between the top three and the bottom tier of Bill Richardson, Joe Biden and Chris Dodd that their hopes for a third-place showing would seem to be dimming.

While a third-place finish will hurt the Democratic front-runner who winds up there, it will still provide a small springboard on the Republican side.

In Iowa, Mike Huckabee and Mitt Romney are battling for first. Romney led early, but polls show Huckabee in the lead now. Neither seems likely to finish third.

That slot is vacant, which is why Fred Thompson, Rudy Guiliani, John McCain and Ron Paul are all rediscovering the joys of Iowa here in the last few days of the caucus campaign.

(Had any one of them paid closer attention to the state earlier, he would be in a better position to take third. But don't ask me to explain the strategic decisions of any of these candidates. They seem to be making them up as they go along.)

Here in the final days, they've each realized that a third-place finish would give them a little boost into New Hampshire and the subsequent contests - and winnow out the fourth-, fifth- and sixth-place winners.

In other words, there is a standby seat on the Republican plane. Welcome back, boys. We know you have many choices for your air travel. Thank you for flying Iowa.

By David Yepsen, Des Moines Register, December 27, 2007