The current discussion of the enthusiasm gap raises the issue of partisan differences in interest and motivation but also seems to have implications for partisan differences in presidential approval. Specifically, an undercurrent of contemporary discussions of the enthusiasm gap is that Democratic prospects are somewhat handicapped due to relatively anemic support for the President Obama among his own base. While I am not aware of long-term historical data on partisan differences in enthusiasm, it is possible to explore this related issue by examining partisan differences in levels of presidential approval.
In the figures below I use Gallup presidential approval data, focusing on polls taken during October of midterm years from 1946 to 2010 (with the exception of 1946, for which I had to use a poll from September). In terms of overall approval, President Obama's rating currently stands at 45%, just about six points lower than the average of 50.7% during the preceding 16 midterms (below). This puts him in a better position than President Bush was in October of 2006 and slightly better off than Presidents Clinton and Reagan were in 1994 and 1982, respectively.
But the question at hand is whether Obama's approval rating is being dragged down due to flagging levels of support from his base. Of course, it is expected that presidents enjoy an advantage among their own partisans, so the best way to answer this question is to examine partisan trends in approval over time. The figure below shows, as expected, presidents do best with their own partisans, worst with the opposition party, and somewhere in between with independents. No surprises there. But there are a couple of noteworthy observations to make about pattern in 2010.
First, it is just not true that Obama has a problem with his base. In fact, compared to previous presidents, he is doing relatively well with his base, with an approval rating among Democrats (80%) that is somewhat higher than the average level of support other presidents got from their own partisans (76%). Obviously, though, running strong among the base is not enough, as President Bush actually did slightly better among his base in 2006, when the Republicans lost 30 House seats. Second, in sharp contrast to his own base, the level of approval among the opposition Republicans (7%) represents an all time low during this time period, rivaled only by president Bush's approval among Democrats in in 2006 (9%). Together, 2006 and 2010 represent a substantial negative shift in support among opposition partisans, one that fits with the general pattern of increased partisanship that has been observed by others. Finally, the president is also running about 10 points behind the long-term average among independents, coming in at 40% approval. While it may be expected that presidents fare poorly among opposition partisans, this tepid level of support among independents--a group that is typically down-the-middle on approval--is taking a toll on the overall level of approval.
Even though the president is doing relatively well among his own partisans, the patterns shown above do jibe fairly well with contemporary discussions of the enthusiasm gap, at least in so far as they show that Republicans are much more united in their opposition to the president than Democrats are in their support of him.