Iowa isn't like Florida or Virginia or North Carolina where the midterm electorate is different enough to swing the elections in the opposite direction than the presidential election results. The 2014 electorate will look similar enough to the 2012 electorate.
There are significant fluctuations in IA. The statewide turnout shifts from around 70% in presidential years (08, 12) to 50% in off years like 2010. In Polk the number of voters dropped from 215 K in 2008 to 162 K in 2010 reflecting the statewide shifts. The missing voters in the off year include disproportionately young voters and other groups that might be expected to be more inclined to vote Dem. It may not be as dramatic as in some bigger cities, but there will be a difference in 2014 from 2012.
