The misimpression that the liberals have taken the reins of the party has become widespread. To take just one representative example: "The mainstream of the party has now veered back toward its more populist and pacifist instincts," Yahoo News' Matt Bai wrote Thursday, characterized by "outright contempt for the wealthy and for conservatives generally." Like others who embrace this analysis, Bai draws the conclusion that this will be an obstacle to the presidential prospects of Hillary Clinton, who is perceived as hawkish, establishmentarian, and friendly to corporate interests.

Many Democratic insiders minimize the party's divide. They note that there's broad ideological agreement on social and cultural issues, from abortion and gay marriage to gun control and immigration. National-security and foreign-policy questions have the power to divide but are no longer litmus tests. Even on economic issues, the party generally speaks with one voice: in favor of universal healthcare, against reducing safety-net programs, for progressive taxation and government-driven economic stimulus. Neera Tanden, president of the Center for American Progress, told me in an email that the Democratic Party just doesn't get hung up on internecine battles these days. "I believe that it's a big-tent party that can and should accommodate centrists and liberals," Tanden said. "That ideological purity has not been a winning strategy for the other side."

But this high-altitude view elides real differences, such as disagreement over how much to raise taxes and on whom, how much to regulate industry, and whether to press not just to preserve but to expand those safety-net programs. (In addition to the Cuomo-de Blasio feud, Warren's signature proposal would increase Social Security benefits, and Obama's push for new free-trade agreements has run into resistance from Senate Majority Leader Harry Reid.) And the divide isn't so much about issues as tone and tactics. The Warrenites harp on the gap between rich and poor and inveigh against big business; the centrists assure their big corporate donors that Democrats can be business-friendly.

The comparison to Republicans is inevitable and instructive. No one seriously doubts anymore that the GOP is badly divided, with a right-wing faction that has virtually declared war on the more moderate establishment. But few of the party's politicians disagree on social or cultural issues (immigration is a notable exception), and the view that taxes should be lower and government smaller is virtually unanimous. What the Ted Cruz faction and the John Boehner faction disagree on is whether the party's rhetoric ought to be conciliatory or scorched-earth, and how far to go—shutting down the government? refusing to raise the debt ceiling?—in pursuit of agreed-upon goals like getting rid of Obamacare. The GOP's divide, like the Democrats', is more about tone than about issues.