In an interview after Alexandria Ocasio-Cortez’s victory in June over incumbent Congressman Joe Crowley, Tom Perez, the chairman of the Democratic National Committee, called the 28-year-old “the future of our party.”

Soon, leading Democratic presidential aspirants Kirsten Gillibrand and Elizabeth Warren had endorsed her signature demand: to “abolish ICE,” the Immigration and Customs Enforcement agency. Even Bernie Sanders, after initial demurrals, called for eliminating “the cruel, dysfunctional immigration system” and Kamala Harris for “starting from scratch” when it came to ICE. Only Cory Booker balked, calling for hearings on whether immigration enforcement “might be achieved better in other ways.” These Democrats had already signed on to other parts of Ocasio-Cortez’s platform: All five had demanded Medicare for All; Sanders, Booker, and Gillibrand had also endorsed a federal jobs guarantee.

These sharp moves to the left are supposed to be good for the country—and for the Democrats. Yet they would likely prove disastrous in a general election. The fact that growing numbers of Democratic politicians seem to support them suggests that they have not figured out how to resurrect themselves as a party. To do that, they need to reclaim many of the voters in the Midwest and Mid-Atlantic who backed Democrats in 2006 and 2008 but sided with Trump in 2016. These kinds of programs will, if anything, drive those voters away.

The political problem for Democrats can be expressed in geometric figures. The older Democratic majority, which dominated American politics from 1930 to 1968, was rooted in the working and middle classes. It was shaped like a pyramid, with Democratic support declining toward the top as income and education rose. Beginning in the 1970s, however, as the white working and middle classes, which had been the bulwark of the old party, began to vacate it, it increasingly resembled an hourglass that bulged with working-class minorities at the bottom and upper-middle-class professionals near the top.

This hourglass coalition, which Ruy Teixeira and I described in our 2002 book, The Emerging Democratic Majority, could win elections as long as Democrats carried about 40 percent (lower in the South but higher elsewhere) of the white working class. In the 2016 presidential election, Hillary Clinton got only 29 percent of these voters. In the crucial swing state of Ohio, she got 33 percent.