In the Iowa caucuses, second choice can be first winner.

It only happens in the Democratic contests, which involve a lot of arguing and realignment; Republican just cast ballots. But as I wrote this morning, candidates have to reach a viability threshold of 15 percent at each caucus site, meaning that voters who favor contenders who don't clear that bar (Biden, Richardson, Kucinich) are often forced to pick a candidate who does (Obama, Edwards, Clinton) in the end.

Understandably, campaigns are obsessed with winning over as many "unviable" voters as they can. All of them know the identities of thousands of supporters of other candidates (they keep track when canvassing). And all of them have armed their precinct captains with specific pitches to sway specific people away from specific candidates. And this year's field is especially fertile, as lower-tier candidates account for the 13 percent of the vote, compared with 5 percent in 2004. 

The wheeling and dealing, in fact, is already underway. It happens every four years--a lower-tier candidate makes a deal with top-tier candidate, then asks his supporters to choose that frontrunner if he's not viable. In 2004, Kucinich did Edwards the favor, and it was a big reason why the North Carolina senator finished such a strong second.

This year's big beneficiary is Obama. On New Years, Kucinich ditched Edwards for the Illinois senator, and today solidly-sourced reports have surfaced in the Washington Post and New York Times of Biden-Obama and Richardson-Obama agreements. Of course, Obama, Biden and Richardson all deny the stories; none of them want to seem as if they're telling Iowans what to do. But if true--even if it doesn't happen in every precinct--this means Obama has a potential head-start with supporters of the two highest polling second-tier candidates, and a third one for good measure. Together, Richardson, Kucinich and Biden average 12 percent of the vote. In a razor-close race, even a small edge in that pool could make a huge difference.