Nate Silver makes a good point:
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. One might likewise have been tempted to consider the combination of the Democrats’ landslide in the 1974 midterms and Jimmy Carter’s ascendancy in 1976 a ‘realignment’. Reagan and FDR, however, were effective Presidents, whereas Carter and Harding were not, quickly managing to relinquish most of what they had gained. Barack Obama, perhaps, may be the first President since Reagan in 1980 to have an opportunity to realign the country; whether or not he’ll do so is another matter.
The Dish 