Katie Martin / The Atlantic

George Washington’s farewell address is often remembered for its warning against hyper-partisanship: “The alternate domination of one faction over another, sharpened by the spirit of revenge, natural to party dissension, which in different ages and countries has perpetrated the most horrid enormities, is itself a frightful despotism.” John Adams, Washington’s successor, similarly worried that “a division of the republic into two great parties … is to be dreaded as the great political evil.”

America has now become that dreaded divided republic. The existential menace is as foretold, and it is breaking the system of government the Founders put in place with the Constitution.

Though America’s two-party system goes back centuries, the threat today is new and different because the two parties are now truly distinct, a development that I date to the 2010 midterms. Until then, the two parties contained enough overlapping multitudes within them that the sort of bargaining and coalition-building natural to multiparty democracy could work inside the two-party system. No more. America now has just two parties, and that’s it.

The theory that guided Washington and Adams was simple, and widespread at the time. If a consistent partisan majority ever united to take control of the government, it would use its power to oppress the minority. The fragile consent of the governed would break down, and violence and authoritarianism would follow. This was how previous republics had fallen into civil wars, and the Framers were intent on learning from history, not repeating its mistakes.

James Madison, the preeminent theorist of the bunch and rightly called the father of the Constitution, supported the idea of an “extended republic” (a strong national government, as opposed to 13 loosely confederated states) for precisely this reason. In a small republic, he reasoned, factions could more easily unite into consistent governing majorities. But in a large republic, with more factions and more distance, a permanent majority with a permanent minority was less likely.

The Framers thought they were using the most advanced political theory of the time to prevent parties from forming. By separating powers across competing institutions, they thought a majority party would never form. Combine the two insights—a large, diverse republic with a separation of powers—and the hyper-partisanship that felled earlier republics would be averted. Or so they believed.

However, political parties formed almost immediately because modern mass democracy requires them, and partisanship became a strong identity, jumping across institutions and eventually collapsing the republic’s diversity into just two camps.

Yet separation of powers and federalism did work sort of as intended for a long while. Presidents, senators, and House members all had different electoral incentives, complicating partisan unity, and state and local parties were stronger than national parties, also complicating unity.

For much of American political history, thus, the critique of the two-party system was not that the parties were too far apart. It was that they were too similar, and that they stood for too little. The parties operated as loose, big-tent coalitions of state and local parties, which made it hard to agree on much at a national level.

From the mid-1960s through the mid-’90s, American politics had something more like a four-party system, with liberal Democrats and conservative Republicans alongside liberal Republicans and conservative Democrats. Conservative Mississippi Democrats and liberal New York Democrats might have disagreed more than they agreed in Congress, but they could still get elected on local brands. You could have once said the same thing about liberal Vermont Republicans and conservative Kansas Republicans. Depending on the issue, different coalitions were possible, which allowed for the kind of fluid bargaining the constitutional system requires.

But that was before American politics became fully nationalized, a phenomenon that happened over several decades, powered in large part by a slow-moving post-civil-rights realignment of the two parties. National politics transformed from a compromise-oriented squabble over government spending into a zero-sum moral conflict over national culture and identity. As the conflict sharpened, the parties changed what they stood for. And as the parties changed, the conflict sharpened further. Liberal Republicans and conservative Democrats went extinct. The four-party system collapsed into just two parties.

The Democrats, the party of diversity and cosmopolitan values, came to dominate in cities but disappeared from the exurbs. And the Republicans, the party of traditional values and white, Christian identity, fled the cities and flourished in the exurbs. Partisan social bubbles began to grow, and congressional districts became more distinctly one party or the other. As a result, primaries, not general elections, determine the victor in many districts.

Over the past three decades, both parties have had roughly equal electoral strength nationally, making control of Washington constantly up for grabs. Since 1992, the country has cycled through two swings of the pendulum, from united Democratic government to divided government to united Republican government and back again, with both sides seeking that elusive permanent majority, and attempting to sharpen the distinctions between the parties in order to win it. This also intensified partisanship.

These triple developments—the nationalization of politics, the geographical-cultural partisan split, and consistently close elections—have reinforced one another, pushing both parties into top-down leadership, enforcing party discipline, and destroying cross-partisan deal making. Voters now vote the party, not the candidate. Candidates depend on the party brand. Everything is team loyalty. The stakes are too high for it to be otherwise.

The consequence is that today, America has a genuine two-party system with no overlap, the development the Framers feared most. And it shows no signs of resolving. The two parties are fully sorted by geography and cultural values, and absent a major realignment, neither side has a chance of becoming the dominant party in the near future. But the elusive permanent majority promises so much power, neither side is willing to give up on it.

This fundamentally breaks the system of separation of powers and checks and balances that the Framers created. Under unified government, congressional co-partisans have no incentive to check the president; their electoral success is tied to his success and popularity. Under divided government, congressional opposition partisans have no incentive to work with the president; their electoral success is tied to his failure and unpopularity. This is not a system of bargaining and compromise, but one of capitulation and stonewalling.

Congressional stonewalling, in turn, leads presidents to do more by executive authority, further strengthening the power of the presidency. A stronger presidency creates higher-stakes presidential elections, which exacerbates hyper-partisanship, which drives even more gridlock.

Meanwhile, as hyper-partisanship has intensified legislative gridlock, more and more important decisions are left to the judiciary to resolve. This makes the stakes of Supreme Court appointments even higher (especially with lifetime tenure), leading to nastier confirmation battles, and thus higher-stakes elections.

See how this all reinforces itself? That’s what makes it so tricky to resolve, at least in a two-party system with winner-take-all elections.

Political science has come a long way since 1787. Had the Framers been able to draw on the accumulated wisdom of today, they would have accepted that it is impossible to have a modern mass democracy without political parties, much as they might have wanted it. Parties make democracy work by structuring politics, limiting policy and voting choices to a manageable number. They represent and engage diffuse citizens, bringing them together for a common purpose. Without political parties, politics turns chaotic and despotic.

The Founders also would have known that plurality elections (whoever gets the most votes wins) tend to generate just two parties, while proportional elections (vote shares in multi-winner districts translate into seat shares) tend to generate multiple parties, with the district size and threshold percentages shaping the number.

But at the time, the Framers believed they could have a democracy without parties, and the only electoral system in operation was the 1430 innovation of plurality voting, which they imported from Britain without debate. It wouldn’t be until the 19th century that reformers came up with new voting rules, and until the 20th century that most advanced democracies moved to proportional representation, supporting multiparty democracies.

Had the Framers accepted the inevitability of political parties, and understood the relationship between electoral rules and the number of parties, I believe they would have attempted to institutionalize multiparty democracy. Certainly, Madison would have. “Federalist No. 10,” with its praise of fluid and flexible coalitions, is a vision of multiparty democracy.

The good news is that nothing in the Constitution requires a two-party system, and nothing requires the country to hold simple plurality elections. The elections clause of the Constitution leaves states to decide their own rules, and reserves to Congress the power to intervene, a power that Congress has used over the years to enforce the very plurality-winner single-member districts that keep the two-party system in place and ensure that most elections are uncompetitive.

If the country wanted to, it could move to a system of proportional representation for the very next congressional election. All it would take is an act of Congress. States could also act on their own.

Multiparty democracy is not perfect. But it is far superior in supporting the diversity, bargaining, and compromise that the Framers, and especially Madison, designed America’s institutions around, and which they saw as essential to the fragile experiment of self-government.

America has gone through several waves of political reform throughout its history. Today’s high levels of discontent and frustration suggest it may be on the verge of another. But the course of reform is always uncertain, and the key is understanding the problem that needs to be solved. In this case, the future of American democracy depends on heeding the warning of the past. The country must break the binary hyper-partisanship so at odds with its governing institutions, and so dangerous for self-governance. It must become a multiparty democracy.

This story is part of the project “The Battle for the Constitution,” in partnership with the National Constitution Center.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.