In the resulting atmosphere of crisis and upheaval, a new coalition can bring a new reconstructive president to power. When that happens, Skowronek wrote, governing priorities are “durably recast,” and a “corresponding set of legitimating ideas becomes the new common sense.” Franklin Delano Roosevelt was a reconstructive president. So was Ronald Reagan. The assumptions of New Deal liberalism governed American politics from 1932 to 1980. The assumptions of the conservative movement have dominated thereafter, though perhaps not for much longer.

Viewed through this schema, Donald Trump’s presidency looks more like the end of a cycle than the end of the Republic. Throughout the 2016 presidential campaign and the early months of the Trump administration, the constitutional law professors Jack Balkin and Sanford Levinson exchanged letters arguing about the durability of our system; the letters will be published this spring as a book, “Democracy and Dysfunction.” Balkin is the more sanguine of the two, in part because he sees Trump fitting into Skowronek’s model.

Trump’s presidency, wrote Balkin, could be what Skowronek called “disjunctive,” meaning one “in which a president allied with an aging political regime promises to restore its dominance and former greatness, is unable to keep all of the elements of his coalition together, and as a result presides over the regime’s dissolution.”

If this analysis is correct, intrepid activists have a chance to decide what comes next. “In the next few election cycles, a new regime will begin, offering the possibility of a new beginning in American politics,” wrote Balkin.

The young progressives pushing the Green New Deal have a similar sense of historic opportunity. Waleed Shahid, communications director for the Justice Democrats — the group that recruited Alexandria Ocasio-Cortez to run for Congress — frames the Green New Deal as an overarching vision for political renewal.