While many political commentators, myself included, have seized upon employment numbers as the key economic indicator on political outcomes in 2010, some political science on the subject finds that unemployment has little to no effect on political outcomes. Instead, a broader measure, income growth, is likely to have the biggest impact:
Even the high unemployment rate may be less important politically than you'd think. Seth Masket, a political scientist at the University of Denver, has found that, in midterm elections since 1950, there's been no correlation between the unemployment rate and election outcomes. The key economic variable for voters, other studies show, has been income growth, or, more specifically, how fast per-capita G.D.P. is rising. In other words, if income growth is brisk enough, Democrats should benefit at the polls even if unemployment stays high.
Even leaving aside the political science, this makes sense intuitively. Unemployment directly affects about one in ten people right now. While that number increases significantly when underemployment, and the impact on families is taken into account, real income affects pretty much everyone who isn't retired. That accounts for three in four Americans--many more than unemployment alone can ever impact.
GDP growth has been pretty robust in the United States over the last two quarters, at 2.2% and 5.6% respectively. Declining immigration during the recession has also slowed population growth. These two trends should result in a significant, upward trending increase in per capita GDP during 2010.
Then again, while per capita GDP should be on the rise in 2010, it has yet to rise for most Americans. Here is the BLS chart on average hourly earnings since early 2008:
Average hourly earnings have not improved much at all, and the situation is not improving. Total hours worked is also stagnant. This implies that the recent improvements in per capita GDP have not yet translated into wages, and thus an improved electoral environment for Democrats.
The stimulus was backloaded with 2010 spending, and Democrats might be able to enact additionally, smaller spending bills to further improve the job situation in 2010. However, this will not help them politically if personal income does not start improving for most Americans. It will likely be that broader measure of personal prosperity that has the most impact on the 2010 elections.