How big a deal is the surprise primary defeat of Representative Eric Cantor, the House majority leader? Very. Movement conservatism, which dominated American politics from the election of Ronald Reagan to the election of Barack Obama — and which many pundits thought could make a comeback this year — is unraveling before our eyes.

I don’t mean that conservatism in general is dying. But what I and others mean by “movement conservatism,” a term I think I learned from the historian Rick Perlstein, is something more specific: an interlocking set of institutions and alliances that won elections by stoking cultural and racial anxiety but used these victories mainly to push an elitist economic agenda, meanwhile providing a support network for political and ideological loyalists.

By rejecting Mr. Cantor, the Republican base showed that it has gotten wise to the electoral bait and switch, and, by his fall, Mr. Cantor showed that the support network can no longer guarantee job security. For around three decades, the conservative fix was in; but no more.

To see what I mean by bait and switch, think about what happened in 2004. George W. Bush won re-election by posing as a champion of national security and traditional values — as I like to say, he ran as America’s defender against gay married terrorists — then turned immediately to his real priority: privatizing Social Security. It was the perfect illustration of the strategy famously described in Thomas Frank’s book “What’s the Matter With Kansas?” in which Republicans would mobilize voters with social issues, but invariably turn postelection to serving the interests of corporations and the 1 percent.