The process works something like this. When parties lose power, activists ascribe the loss to the ideological impurity of their incumbent president. In so doing, they vent the frustrations they kept bottled up while their side was in power. Since defeat frees them from the messy business of governing, ideological purity suddenly becomes easier. And since defeat usually hits party moderates disproportionately hard, the opponents of purity usually hold less sway…

The one major advantage today’s Republicans have over the Democrats of the early 1970s is the economy: If it is actually worse in 2012 than it is today, all bets are off. But if it improves, even modestly, Republicans are likely in for the kind of rude awakening that Democrats experienced in 1972. The reason is that in their fervor to make their parties ideologically pure, the Tea Partiers, like the McGovernites, have not noticed that the bulk of the country is actually moving the other way. In retrospect, the story of the Vietnam years is not the rise of the anti-war left; it was the rise of the suburban Sun Belt, that rapidly growing swath of the country that would elect Reagan, Gingrich, Bush, and DeLay. The McGovernites were so angry that Kennedy, Johnson, and Humphrey had compromised their liberalism that they didn’t notice that the fastest growing share of the electorate didn’t want any liberalism at all.

Similarly, the Tea Party is today garnering all the headlines, but the rising demographic force in today’s politics is not aging white conservatives, but Hispanics and Millennials, two rapidly growing portions of the electorate that are uncomfortable with any right-leaning ideology at all, let alone the right-wing purism of Palin and company.