In an important 2004 paper pertinent to this discussion, "Partisan Politics and the U.S. Income Distribution," Larry M. Bartels surveyed fifty-three years of presidential history, 1948-2001, to measure partisan differences in economic performance. He found that all income groups did better under post-war Democratic presidents, with those in the bottom 20 percent seeing their pre-tax incomes rise four times as much under the Democrats as under the Republicans. That is because of the better overall economic performance turned in by the Democrats, who averaged 4.84 percent unemployment and 4.08 percent GDP growth to the Republicans’ 6.35 percent and 2.86 percent. Only with inflation and only by a nose—3.97 percent to 3.95 percent—did the Republicans do better. How, then, did they manage to win or hold office?
Correlations between the economy and the presidential vote are weaker than between the economy and the congressional vote. Other issues—war and peace—and the personalities of the candidates can play major roles. But Republican presidents have also timed the political cycle better than the Democrats. In election years, at every level, income rose 2 percent under the Republicans but only 1 percent under the Democrats. Will the Republicans be able to game cycle again in 2008? In an economy experiencing both rising inflation and unemployment—stagflation—cutting taxes or increasing spending, standard GOP tactics ahead of election-years, will only stimulate inflation, reducing real incomes. By swelling the deficit, they will also put more upward pressure on interest rates, increasing unemployment. Surely it is instructive that the only recent presidents to preside over stagflation, Gerald Ford and Jimmy Carter, both lost.
The economy—understood as personal incomes going up or down and unemployment going up or down—is the classic "valence-issue" in politics. "Instead of ‘position’ issues, where one party favors policy X and the other party favors policy Y…'valence' issues chiefly hinge on perceived government management: my party can manage the economy or the war, for example, better than your party has been doing," David R. Mayhew, a Yale political scientist, explains in Electoral Realignments (2002). "The more one examines American electoral history, the more it seems to tilt toward valence-issue as opposed to position-issue junctures." In his 1963 paper introducing the term, Donald E. Stokes defined "valence-issues" as "those that merely involve the linking of the parties with some condition that is positively or negatively valued by the electorate."
If this excursion into political science has any relevance for Democratic electioneering, it may be this: downplay "position-issues"; they leave you open to attack. Instead link the Republicans to "conditions negatively valued by the electorate"—incompetent management of the government and falling real incomes or rising unemployment or both. Make the 2006 and 2008 elections referenda on a record of miserable failure.