In the top graph, if you look in the upper left-hand corner--low unemployment and strong support for McCain, you find a collection of mostly Republican states: Wyoming, Oklahoma, Nebraska, North and South Dakota, Utah. In the lower right-hand corner--high unemployment and low support for McCain, you find a collection of Democratic and competitive states: Michigan, Rhode Island, California, Oregon, and Nevada. And the same pattern holds for the bottom figure. In other words, what appears to be a relatively weak, negative relationship between unemployment and support for the incumbent party candidate, likely just reflects the coincidental overlap of unemployment and partisan tendencies. Indeed, both relationships are spurious and disappear once you take into account the partisan predispositions (Republican share of the 2008 vote) of the states. In fact, the partial correlation for the September unemployment rate is positive (ryx,z=.20), though not significant.
And it turns out the 2008 is not the only instance of null effects from unemployment. The Table below provides some findings from simple regression models in which the incumbent party vote share is regressed on either the September unemployment rate or the change in the unemployment rate between January and September (separate models), along with the statewide vote share for the incumbent party candidate in the previous election. The cell entries are the unstandardized regression coefficients for each year, along with an asterisk to indicate if the slope is significant at the .05 level.
Simply put, there is nary a shred of evidence to suggest that the unemployment outlook in the states has anything to do with state-level outcomes in presidential elections.
In fact, there are only two cases of significant effects--both for the September unemployment rate--and one of those is a positive coefficient, suggesting that the incumbent candidate, Jimmy Carter, benefited from higher unemployment! While one could make a policy-oriented argument in favor of this, it seems like a bit of a stretch. Te most obvious conclusion to draw from this table is that state-to-state variations in unemployment are not likely to have much impact on how the states vote this November.
This is not to say that unemployment doesn't have electoral repercussion. In fact, as I showed last summer, changes in the national unemployment are closely tied to election outcomes. Simply put, presidential elections are national elections and it is national conditions--not state-level variation around those conditions--that drive them.