It's no surprise that Gov. Scott Walker won the recall. Polls had shown him ahead for some time. The question here is: did the spending make a difference? In such quandaries, a counterfactual is the best way to demonstrate causality. For example, would Walker have won....if he had raised less money? ...or if he had raised a higher proportion of his money from in-state donors? ...or if Barrett had raised more? Seth's attempt to capture such a counterfactual using the 2010 election is reasonable, perhaps because it some of the only evidence we have. I think some readers have found this unsatisfying because the implication is that the two years of intervening political turmoil were, perhaps, meaningless (at least in terms of affecting political change in the form of an election outcome).
My colleague in Wisconsin, Nils Ringe, pointed out an intriguing observation: Barrett received about as many votes as there were signatures on the Walker recall petition (around a million signatures and votes). It seems that nearly everyone who voted for Barrett, perhaps, signed the petition to recall the Governor. There are two ways to read this, with respect to our question above: 1. If Barrett had spent more money (equal to Walker) he could have mobilized more voters--those who supported him but hadn't signed the petition--and surpassed Walker. Or, 2. Barrett successfully mobilized all the voters he possibly could have to support his cause.
Do we have any evidence for either of these? Turnout may be a good indicator of which interpretation is more valid. If turnout was low, then interpretation 1 may carry more weight. High turnout might indicate that interpretation 2 is more plausible. Turnout in Tuesday's election was near 60 percent. In historical terms in Wisconsin, this was not record breaking (in 1960 it is estimated that 72 percent of eligible voters cast ballots in the Kennedy-Nixon race), but it is quite high, and much higher than typical, non-national elections in the United States. I find this evidence more consistent with the claim #2 above: just maybe Barrett was able to maximize the mobilization for his candidacy, both in the petition phase and the ballot phase of the recall effort. This does not mean that more money wouldn't have mobilized even more voters, but given the other evidence discussed in prior posts, it seems Barrett may have maxed out his total support (financial and otherwise).