[...] American political institutions actually require precisely the opposite to work: a near-angelic degree of social cohesion (if not agreement on political ends) among empowered elites. The cold-war order had in fact been forged on two related facts. The first was an organized working class that helped deliver the supermajorities needed to defeat barriers to mass democracy in the 1930s, and then mustered enough electoral strength in the decades that followed to expand, or at least protect, the social safety net their efforts had secured. Just as essential, the confrontation with the Soviet Union fostered cohesion among political elites in ways that produced the conditions for compromise, most dramatically evidenced during the period of 1960s civil rights legislation. When the Republican senator Everett Dirksen helped break the Southern filibuster of the 1964 Civil Rights Act, declaring, “The time has come for equality of opportunity. . . . It will not be stayed or denied,” he was speaking the same liberal universalist language as Lyndon Johnson and was motivated, regardless of the partisan divide, by much the same vision of the country and its global mission.

With working-class organizations weakened, it has become hard to see how any political coalition can elect a supermajority capable of overcoming the Constitution’s roadblocks. At the same time, the US’s enemies, from marginal global players like North Korea to weak nonstate actors like al Qaeda or ISIS, hardly present an existential competitor in the style of the USSR. There are no longer external incentives for elite agreement. Instead, a combination of intense party polarization and the profound influence of money have left the legislative branch constitutively unable to confront fundamental social issues. And as Obama’s post-2010 time in office made clear, even the ever-more-powerful executive branch is limited when it comes to reshaping domestic policy.