As for a president's supporters, Sabato said how they normally find themselves pleased with items A, B and C -- but let down by D, E and F. "Well, how does the human mind work? It's focused on D-E-F. That tends to lower the president's partisans' intentions to vote."
So what can Republicans do to sustain this trend, and what can Democrats do to turn it around? "Well politically obviously they [Republicans] have to continue to stir their base in opposition to President Obama and Congressional Democrats, which isn't hard," said Sabato. "That's a pretty easy task. Being in opposition is just easier than governing, and that's the fact of the matter for either side."
"The Democrats -- we've talked a million times about passing health care reform to give the base something to be happy about." However, Sabatao explained why even this won't be enough: "They're not going to be wildly enthusiastic about it, because it will be a product of compromise. So I don't know if the simple passage of health care reform will be enough to do it."
The economy will also be an important factor. Sabato added that while unemployment is not likely to turn around in time for 2010, other economic indicators, such as per-capita and per-family income, could go up. However, the Democrats will still have to deal with unemployed supporters who might not go for the Republicans -- but won't show up for the Dems, either.
"When you're turned off to the system, you don't necessarily vote for the opponent," he said. "You don't abandon your party ID. You might not just show up to vote. It's easier to move a half step than a whole step."