Read: The liberal Millennial revolution

Representative Alexandria Ocasio-Cortez is often described as a radical, but the data show that her views are close to the median for her generation. The Millennials and Generation Z—that is, Americans aged 18 to 38—are generations to whom little has been given, and of whom much is expected. Young Americans are burdened by student loans and credit-card debt. They face stagnant real wages and few opportunities to build a nest egg. Millennials’ early working lives were blighted by the financial crisis and the sluggish growth that followed. In later life, absent major changes in fiscal policy, they seem unlikely to enjoy the same kind of entitlements enjoyed by current retirees.

Under different circumstances, the under-39s might conceivably have been attracted to the entitlement-cutting ideas of the Republican Tea Party (especially if those ideas had been sincere). Instead, we have witnessed a shift to the political left by young voters on nearly every policy issue, economic and cultural alike.

As a liberal graduate student and a conservative professor, we rarely see eye to eye on politics. Yet we agree that the generation war is the best frame for understanding the ways that the Democratic and Republican parties are diverging. The Democrats are rapidly becoming the party of the young, specifically the Millennials (born between 1981 and 1996) and Gen Z (born after 1996). The Republicans are leaning ever more heavily on retirees, particularly the Silent Generation (born before 1945). In the middle are the Gen Xers (born between 1965 and 1980), who are slowly inching leftward, and the Baby Boomers (born between 1946 and 1964), who are slowly inching to the right.

This generation-based party realignment has profound implications for the future of American politics. The generational transition will not dramatically change the median voter in the 2020 election—or even in 2024, if turnout among young voters stays close to the historical average. Yet both parties are already feeling its effects, as the dominant age cohort in each party recognizes its newfound power to choose candidates and set the policy agenda. Drawing on opinion polls and financial data, and extrapolating historical trends, we think that young voters’ rendezvous with destiny will come in the mid to late 2020s.

Read: Why America is moving left

Today, the older generations have a lock on political power in Washington. House Speaker Nancy Pelosi and Senate Majority Leader Mitch McConnell are members of the Silent Generation. So are Joe Biden and Bernie Sanders, who lead in nearly every poll of the 2020 Democratic primary. President Donald Trump and the median senator and representative are Boomers. Of the nine justices on the Supreme Court, two are from the Silent Generation and six are Boomers. Yet the median American is 38—a Millennial.

Over the past year, the Democratic Party’s geriatric leadership has begun to feel the ground moving beneath its feet. For decades, moderate Democrats have kept a tight grip on the party’s platform. The 2018 midterm elections were a watershed. Boomers and members of the Silent Generation still make up more than three-fifths of the party’s House members and hold all major leadership roles. But newly elected members—including 14 Millennials and 32 Gen Xers—are driving the conversation on policy, from Ocasio-Cortez’s Green New Deal to a recent resolution to withdraw support from Saudi Arabia’s war in Yemen.