Toward the end of his new book, “R.I.P. G.O.P.,” the renowned Democratic pollster Stanley Greenberg makes a thrilling prediction, delivered with the certainty of prophecy. “The year 2020 will produce a second blue wave on at least the scale of the first in 2018 and finally will crash and shatter the Republican Party that was consumed by the ill-begotten battle to stop the New America from governing,” he writes.

It sounds almost messianic: the Republican Party, that foul agglomeration of bigotry and avarice that has turned American politics into a dystopian farce, not just defeated but destroyed. The inexorable force of demography bringing us a new, enlightened political dispensation. Greenberg foresees “the death of the Republican Party as we’ve known it,” and a Democratic Party “liberated from the nation’s suffocating polarization to use government to advance the public good.” I’d like to believe it, and maybe you would too. But should we?

This is not the first time that experts have predicted the inevitable triumph of progressive politics. Seventeen years ago, John Judis and Ruy Teixeira published “The Emerging Democratic Majority,” which argued that the country was on the cusp of a liberal political realignment driven by growing diversity, urbanization and gender equality. In sheer numerical terms they were right; between then and now the Republican Party won the presidential popular vote only once, in 2004. But Republicans still have more power than Democrats, and in 2017, Judis disavowed his book’s thesis, arguing that only populist economics could deliver Democratic victories.

As it happens, Greenberg, who became famous as Bill Clinton’s pollster in 1992 and consulted for Hillary Clinton in 2016, told me he used to “shudder” at the “Emerging Democratic Majority” analysis. “I’m used to campaigns in which you impact what’s going to happen,” he said. “The idea that it’s just going to happen because of trends is dangerous. And it was dangerous with Hillary.”