For liberals, the Obama years were supposed to mark a return to progressive government activism, a latter-day Great Society. But the Great Society, it’s crucial to remember, was launched in the mid-1960s, at the high noon of American optimism about our position in the world. What destroyed it, among other things, was the painful realization, by the early 1970s, that American resources were more finite, and America’s international position more fragile, than Johnson and his whiz-kid advisers had understood. Similarly, it is now clear that today’s political environment is less like the early and mid-1960s, that era of liberal optimism—or even the 1980s, which were dominated by Reagan’s conservative optimism—than by the deeply pessimistic 1970s. President Obama, like presidents Nixon, Ford, and Carter, will be defined by how he manages the politics of decline.