Nate Silver says it’s too soon to tell if we’ve just witnessed a “realigning” election:
Since the turn of the last century, there have been 11 cases in which the presidency changed parties: 1912 (Wilson), 1920 (Harding), 1932 (Roosevelt), 1952 (Eisenhower), 1960 (Kennedy), 1968 (Nixon), 1976 (Carter), 1980 (Reagan), 1992 (Clinton), 2000 (Bush), and 2008 (Obama). In 9 of the 11 cases, the party winning the presidency had also made substantial gains in the Congress as compared with four years’ earlier (although not necessarily as compared with two years’ earlier). The two exceptions were the last two party changes before Obama: Clinton in 1992, when the Democrats were pretty much treading water in the Congress, and Bush in 2000, when the Republicans were doing likewise.
What ultimately distinguishes the elections that are considered to have been realignments is the efficacy of the governance of the rising party, rather than the force with which said party took office. Ronald Reagan and FDR, famously, had coattails — but so did Warren G. Harding, who brought the Republicans a net gain of 123 (!) seats in the House in 1920.
I think the better way to put the point is simply to agree with David Mayhew that there isn’t really any such thing as a “realigning election.” Or, to put it in perhaps a more Rortian way, to say that questions about realignments aren’t useful questions to ask. If presidential election outcomes were completely random the odds would still overwhelmingly favor the emergence of Democratic and Republican “clusters” and you could choose to interpret the beginning election of some cluster as a “realigning” random outcome. But why would you want to?
Of course election outcomes aren’t random. But they’re determined largely by events and, needless to say, the events of 2010, 2012, 2016 and so forth haven’t happened yet. Whether big Democratic wins in 2006 and 2008 will be followed by consolidation of power or backlash depends entirely on what happens in the future and not at all on factors you can discern by peering into the election results.