The fit of soul-searching provoked by Donald Trump has, at times, seemed overwrought. “We’re toxic in the Midwest, and we’re toxic in the South,” Representative Tim Ryan, the young backbencher from Ohio, warned on November 30, 2016, challenging Nancy Pelosi for the leadership of the Democratic caucus. Democrats, he averred, would be “wiped out” if they did not shift directions, relegating themselves to a narrow, though populous, corridor along the coasts. The existential rhetoric was not unusual, given the party had just lost the White House, and had already relinquished control of the House, the Senate, and two-thirds of all state houses. More surprising, however, has been the equally apocalyptic rhetoric coming from both sides of the G.O.P. In just the past few weeks, Senator Jeff Flake has likened Trump rallies to the “spasms of a dying party,” while Sean Hannity, for entirely opposite reasons, expressed a similar sentiment: “[the Republican Party] is a dead party. They are morally corrupt, they are weak,” he told Breitbart News Tonight, accusing the establishment of betraying its base. “They are ineffective, they’re visionless, and they have no identity.”

It is tempting to dismiss all this as arid political posturing, since in a two-party system, it seems mathematically impossible for both parties to be failing at the same time. But in fact, that is exactly what is happening, and it portends significant changes to our political system. For the last half century, the binary structure of American politics has been undergoing a dramatic change. In the 1960s, roughly half the country identified as Democrats and more than one quarter as Republicans. Only a modest minority, roughly 20 to 22 percent, thought of themselves as Independents. By 1988, when Gallup first started tracking this on a regular basis, the numbers had evened out, with about 36 percent of respondents identifying themselves as Democrats, 33 percent as Independents, and 31 percent as Republicans. But by 2015, Independents had become by far the largest group, at 42 percent, with Democrats and Republicans lagging far behind. The slow growth of Independents over the last half century, and the flight from both political parties, has been consistent through good times and bad, through popular presidencies and unpopular ones, and seems to be without any upward bounds at the moment.

In this age of hyperpolarization, when angry voices from both the right and the left control the public narrative, Independents are discussed far less than their growing numbers alone might suggest. In part, this is due to the belief among many political strategists and political scientists that most Independents behave like partisans, voting predictably for one side or the other. That is true for some, but Independents also encompass true moderates, people who are cross-polarized (liberal on some issues, conservative on others), and some who are just politically ambivalent or disconnected. But despite the rather disparate and somewhat motley nature of Independents, there is a common thread that binds them together: they are increasingly embarrassed by the political parties and increasingly sure that the two main political parties do not serve them and the larger society. And it is likely that this group will continue to grow. Only 37 percent of voters hold positive views of Democrats, and only 30 percent are sweet on the Republicans, both quarter-century lows. Every congressional sexual harassment scandal, Twitter feud, or broken promise fuels their disenchantment. It is possible, maybe even probable, that the number of self-identified Independents will surpass 50 percent this year.

There are, of course, major structural impediments to a viable third party in U.S. politics. The Democratic and Republican national committees have access to hundreds of millions of dollars in cash, can activate tens of thousands of volunteers, and are incentivized to fundraise off the churn of constant, bipolar combat. Donor money flows to these two poles because that is where it is most effective. And, when push comes to shove, most Independents are actually partisans who will support one party or the other. Attempts by centrists to forge a “third way,” as one recently derided effort has been called, have failed to find a natural constituency outside of Acela Corridor elites in New York and Washington.

Still, in the longer term, it is increasingly hard to justify the two major parties—or at least the system that sustains them—when most of the American public would rather wear a paper bag over their heads than be associated with either. The fact that both parties are increasingly out of step with the broader public has not been lost on some senior party officials. Flake’s comments echoed similar, though less sharply articulated concerns from conservative luminaries such as Mitt Romney, George W. Bush, and Senator Bob Corker, and it is hard to argue with that observation, given the G.O.P.’s narrowing appeal to a narrowing part of the electorate. While Flake’s comment might cheer some Democrats, the fact that the Democrats have lost so much to this “dying party” does not speak well of its own electoral and intellectual health. There is an inherent instability in a system of declining loyalties, and that could mean, in very short order, seismic changes in our political system.