Although it may be an unsatisfying one, the correct answer is probably that the election will say little about the future of the Republican and Democratic parties. However, it's likely that either party, having won the presidency in 2012, will draw inordinately sweeping conclusions from it. In examining whether Obama or Romney is more likely to win in 2012, we saw how Democrats historically have a strong tendency to overestimate their candidates' chances of winning. But the temptation to find long-term trends in a few recent data points--usually selectively chosen--applies to both parties.
After George W. Bush won reelection in 2004, the Republican Party was very optimistic about its future. It had scored three victories in a row, prevailing in 2000, the 2002 midterms, and 2004. Republicans had won most of the recent presidential elections: 5 of the last 7 (from 1980-2004) or 7 of the last 10 (1968-2004). Some Republican commentators penned editorials giving Democrats thoughtful advice on how the Democratic Party might fix itself, for the sake of the two-party system.
Only four years later, after Barack Obama won in 2008, the Democrats had a similar attitude. Without either party being aware of the irony, some Democrats wrote similar editorials warning that the Republican Party was in danger of becoming a regional party or entering the political wilderness for an extended period. The most optimistic Democrats opined that demographic changes (i.e. an increased Hispanic population) would lead to an inevitable, permanent Democratic majority. As before, the victorious party was chastened by a crushing mid-term defeat two years later.
Regardless of who wins in 2012, the triumphant party will find ample data to support their optimistic projections. First, let's consider what the "data" will show if Romney wins. The Republican Party will have won 8 out of the last 12 presidential elections. The record will be even worse for liberal Democrats during the same period; with Bill Clinton classified as a moderate, liberals will have won only 2 out of the last 12 elections--both being repudiated after a single term.
If Obama wins reelection, Democrats will be able to paint the past in equally rosy terms: They will have won the popular vote in 5 of the last 6 presidential elections. It will also have been nearly a quarter-century since a Republican presidential candidate last won by 5 points or more (1988). Meanwhile, political scientists will also begin touting the advantages of incumbency, since 4 of the last 5 presidents will have been two-termers.
The reason why observers should be skeptical in both cases is that the conclusions--"Republicans always win" or "Democrats always win"--will hinge on one data point: The winner of the 2012 election. Clearly, if one party can claim supremacy, it shouldn't be possible for the other party to claim supremacy by winning one election.
