With the top three Democrats running so tight in Iowa, it's becoming clear that caucus goers whose first-choice candidates don't clear the 15 percent bar in their precincts could decide the outcome with their subsequent vote. We're already seeing signs of the growing obsession with how this complicated game theory might play out. In the column I posted earlier, Adam Nagourney notes that Dennis Kucinich's second-choicers could give John Edwards a key lift, as they did in 2004. Via Ambinder, a new McCain memo boasts that he's the number-two choice of 45 percent of Romney supporters. And via Pat Healy at The Caucus, check out Hillary Clinton wooing the presumed "experience" voters backing Dodd, Biden and Richardson:

“Now there is a funny argument in fashion these days – it goes something like this — those of us who have been fighting and winning these battles are not the right ones to push our country forward,” Mrs. Clinton said. “The argument suggests that people like me, and Governor Richardson, and Senator Dodd and Senator Biden, are somehow disqualified from making the changes that American needs, even though we’ve been doing that for decades.”

(Pause for analysis: Part of Mrs. Clinton’s strategy to win the Jan. 3 Iowa caucuses is to woo supporters away from Messrs. Richardson, Dodd and Biden if those men do not get 15 percent of the caucus night vote in individual precincts; if they fail to meet that threshold, the supporters will go to another candidate, and Mrs. Clinton is trying to improve her chances at being these voters’ second choice.)

 --Michael Crowley