Well, it worked. Ever since the McCain campaign put Arizona in a festive pink on its electoral map, Democratic blogs are starting to pick up and run with the notion that Arizona is a swing state. The warrant for the claim is pretty thin -- an internal poll leaked by a Democratic congressional candidate showed McCain ahead by just 5 points in an R+6 district. Against that, we have a relative abundance of statewide polling showing Obama no closer than 9 points (and often down by more than that) and the fact that it's McCain's home state.
The home state effect seems generally to be on the order of 6-7 points, but can vary a lot from candidate to candidate and state to state. It might be weaker for McCain than for some other candidates, as he tends more to be a United States Senator than someone who porkbarrels for his home state.
Still, even without that home state effect, Arizona would lag a few points behind pickup opportunities like Colorado, New Mexico and Nevada, largely because of its large retiree population. Is it possible that Obama could win Arizona? Sure (although our model assigns him only a 4 percent chance). Is Arizona likely to make the difference between winning and losing the election? Probably not.
Just for our collective edification, however, you can construct some pure Western strategies for Obama that come up with winning electoral margins. Let's say that Obama loses Ohio and Michigan, but wins Iowa, and everything East of the Mississippi goes as it did in 2004. If Obama sweeps the small "sorta, kinda, maybe" Western states that are polling in the single-digits -- these are Montana, Alaska, and North Dakota -- plus the more talked-about Colorado, Nevada and New Mexico, that would get him to 271 EV. So would Colorado, Nevada, New Mexico and Arizona. But we're a long way from being able to declare the state competitive.