Adam Nagourney thinks it might happen:

That is a very real possibility, given the apparent strength of Mr. Obama and Mr. Edwards and the way the caucuses work. Under the rules, a candidate who receives fewer than 15 percent of the votes in a particular precinct on caucus night is deemed unviable there, and the candidate’s supporters are free to support someone else.

In 2004, Mr. Edwards picked up significant support when supporters of Representative Dennis Kucinich of Ohio cast their lot with Mr. Edwards in precincts where they could not reach the 15 percent threshold themselves. Mr. Kucinich is running again this time.

Mrs. Clinton could probably survive a second-place showing here, given her strength in New Hampshire and her considerable financial assets. But a third-place showing by Mrs. Clinton would be a game-changer.

 --Michael Crowley