I feel as if I'm rerunning all my Iowa greatest hits today, but just a quick one: Iowa isn't everything, and isn't nothing.
So Brad Plumer notices that Iowa winners only get the nomination some of the time, which if you extend the logic winds up with Erik Loomis focusing on Pat Robertson and Pat Buchanan and calling the whole thing a "clown show" best ignored.
They're missing the point. One more time: Iowa is only part of the process, but it's an important part. It can kill off campaigns that appeared to be strong, such as John Glenn in 1984 and Phil Gramm in 1996. It can boost previously obscure people into real contention, such as Gary Hart in 1984 and John Edwards in 2004.
Iowa doesn't do that all by itself. It does it in conjunction with what party actors have done before, and what party actors and other states do later. Even when it wraps up the nomination -- as it did for George W. Bush in 2000 -- it doesn't do that by itself. But yes, where you finish in Iowa really can sometimes affect the results of the nomination, all else equal. Affect, not determine.