The United States has experienced deep political turmoil several times before over the past century. The Great Depression caused Americans to doubt the country’s economic system. World War II and the Cold War presented threats from global totalitarian movements. The 1960s and ’70s were marred by assassinations, riots, a losing war and a disgraced president.

These earlier periods were each more alarming in some ways than anything that has happened in the United States recently. Yet during each of those previous times of tumult, the basic dynamics of American democracy held firm. Candidates who won the most votes were able to take power and attempt to address the country’s problems.

The current period is different. As a result, the United States today finds itself in a situation with little historical precedent. American democracy is facing two distinct threats, which together represent the most serious challenge to the country’s governing ideals in decades.

The first threat is acute: a growing movement inside one of the country’s two major parties — the Republican Party — to refuse to accept defeat in an election.

The violent Jan. 6, 2021, attack on Congress, meant to prevent the certification of President Biden’s election, was the clearest manifestation of this movement, but it has continued since then. Hundreds of elected Republican officials around the country falsely claim that the 2020 election was rigged. Some of them are running for statewide offices that would oversee future elections, potentially putting them in position to overturn an election in 2024 or beyond.

“There is the possibility, for the first time in American history, that a legitimately elected president will not be able to take office,” said Yascha Mounk, a political scientist at Johns Hopkins University who studies democracy.

The second threat to democracy is chronic but also growing: The power to set government policy is becoming increasingly disconnected from public opinion.

The run of recent Supreme Court decisions — both sweeping and, according to polls, unpopular — highlight this disconnect. Although the Democratic Party has won the popular vote in seven of the past eight presidential elections, a Supreme Court dominated by Republican appointees seems poised to shape American politics for years, if not decades. And the court is only one of the means through which policy outcomes are becoming less closely tied to the popular will.

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Two of the past four presidents have taken office despite losing the popular vote. Senators representing a majority of Americans are often unable to pass bills, partly because of the increasing use of the filibuster. Even the House, intended as the branch of the government that most reflects the popular will, does not always do so, because of the way districts are drawn.

“We are far and away the most countermajoritarian democracy in the world,” said Steven Levitsky, a professor of government at Harvard University and a co-author of the book “How Democracies Die,” with Daniel Ziblatt.

The causes of the twin threats to democracy are complex and debated among scholars.

The chronic threats to democracy generally spring from enduring features of American government, some written into the Constitution. But they did not conflict with majority opinion to the same degree in past decades. One reason is that more populous states, whose residents receive less power because of the Senate and the Electoral College, have grown so much larger than small states.

The acute threats to democracy — and the rise of authoritarian sentiment, or at least the acceptance of it, among many voters — have different causes. They partly reflect frustration over nearly a half-century of slow-growing living standards for the American working class and middle class. They also reflect cultural fears, especially among white people, that the United States is being transformed into a new country, more racially diverse and less religious, with rapidly changing attitudes toward gender, language and more.

The economic frustrations and cultural fears have combined to create a chasm in American political life, between prosperous, diverse major metropolitan areas and more traditional, religious and economically struggling smaller cities and rural areas. The first category is increasingly liberal and Democratic, the second increasingly conservative and Republican.

The political contest between the two can feel existential to people in both camps, with disagreements over nearly every prominent issue. “When we’re voting, we’re not just voting for a set of policies but for what we think makes us Americans and who we are as a people,” Lilliana Mason, a political scientist and the author of “Uncivil Agreement: How Politics Became Our Identity,” said. “If our party loses the election, then all of these parts of us feel like losers.”

These sharp disagreements have led many Americans to doubt the country’s system of government. In a recent poll by Quinnipiac University, 69 percent of Democrats and 69 percent of Republicans said that democracy was “in danger of collapse.” Of course, the two sides have very different opinions about the nature of the threat.

Many Democrats share the concerns of historians and scholars who study democracy, pointing to the possibility of overturned election results and the deterioration of majority rule. “Equality and democracy are under assault,” President Biden said in a speech this month in front of Independence Hall in Philadelphia. “We do ourselves no favor to pretend otherwise.”

Many Republicans have defended their increasingly aggressive tactics by saying they are trying to protect American values. In some cases, these claims rely on falsehoods — about election fraud, Mr. Biden’s supposed “socialism,” Barack Obama’s birthplace, and more.

In others, they are rooted in anxiety over real developments, including illegal immigration and “cancel culture.” Some on the left now consider widely held opinions among conservative and moderate Americans — on abortion, policing, affirmative action, Covid-19 and other subjects — to be so objectionable that they cannot be debated. In the view of many conservatives and some experts, this intolerance is stifling open debate at the heart of the American political system.

The divergent sense of crisis on left and right can itself weaken democracy, and it has been exacerbated by technology.

Conspiracy theories and outright lies have a long American history, dating to the personal attacks that were a staple of the partisan press during the 18th century. In the mid-20th century, tens of thousands of Americans joined the John Birch Society, a far-right group that claimed Dwight Eisenhower was a secret Communist.

Today, however, falsehoods can spread much more easily, through social media and a fractured news environment. In the 1950s, no major television network spread the lies about Eisenhower. In recent years, the country’s most watched cable channel, Fox News, regularly promoted falsehoods about election results, Mr. Obama’s birthplace and other subjects.

These same forces — digital media, cultural change and economic stagnation in affluent countries — help explain why democracy is also struggling in other parts of the world. Only two decades ago, at the turn of the 21st century, democracy was the triumphant form of government around the world, with autocracy in retreat in the former Soviet empire, Argentina, Brazil, Chile, South Africa, South Korea and elsewhere. Today, the global trend is moving in the other direction.

In the late 1990s, 72 countries were democratizing, and only three were growing more authoritarian, according to data from V-Dem, a Swedish institute that monitors democracy. Last year, only 15 countries grew more democratic, while 33 slid toward authoritarianism.

Some experts remain hopeful that the growing attention in the United States to democracy’s problems can help avert a constitutional crisis here. Already, Donald Trump’s efforts to overturn the 2020 election failed, partly because of the refusal of many Republican officials to participate, and both federal and state prosecutors are investigating his actions. And while the chronic decline of majority rule will not change anytime soon, it is also part of a larger historical struggle to create a more inclusive American democracy.

Still, many experts point out that it is still not clear how the country will escape a larger crisis, such as an overturned election, at some point in the coming decade. “This is not politics as usual,” said Carol Anderson, a professor at Emory University and the author of the book, “One Person, No Vote,” about voter suppression. “Be afraid.”

The Will of the Majority

The founders did not design the United States to be a pure democracy.

They distrusted the classical notion of direct democracy, in which a community came together to vote on each important issue, and believed it would be impractical for a large country. They did not consider many residents of the new country to be citizens who deserved a voice in political affairs, including Natives, enslaved Africans and women. The founders also wanted to constrain the national government from being too powerful, as they believed was the case in Britain. And they had the practical problem of needing to persuade 13 states to forfeit some of their power to a new federal government.

Instead of a direct democracy, the founders created a republic, with elected representatives to make decisions, and a multilayered government, in which different branches checked each other. The Constitution also created the Senate, where every state had an equal say, regardless of population.

Pointing to this history, some Republican politicians and conservative activists have argued that the founders were comfortable with minority rule. “Of course we’re not a democracy,” Senator Mike Lee of Utah has written.

But the historical evidence suggests that the founders believed that majority will — defined as the prevailing view of enfranchised citizens — should generally dictate national policy, as George Thomas of Claremont McKenna College and other constitutional scholars have explained.

In the Federalist Papers, James Madison equated “a coalition of a majority of the whole society” with “justice and the general good.” Alexander Hamilton made similar points, describing “representative democracy” as “happy, regular and durable.” It was a radical idea at the time.

For most of American history, the idea has prevailed. Even with the existence of the Senate, the Electoral College and the Supreme Court, political power has reflected the views of people who had the right to vote. “To say we’re a republic not a democracy ignores the past 250 years of history,” Mr. Ziblatt, a political scientist at Harvard University, said.

Before 2000, only three candidates won the presidency while losing the popular vote (John Quincy Adams, Rutherford Hayes and Benjamin Harrison), and each served only a single term. During the same period, parties that won repeated elections were able to govern, including the Democratic-Republican Party of Thomas Jefferson’s time, the New Deal Democrats and the Reagan Republicans.

The situation has changed in the 21st century. The Democratic Party is in the midst of a historic winning streak. In seven of the past eight presidential elections, stretching back to Bill Clinton’s 1992 victory, the Democratic nominee has won the popular vote. Over more than two centuries of American democracy, no party has previously fared so well over such an extended period.

Yet the current period is hardly a dominant Democratic age.

What changed? One crucial factor is that, in the past, the parts of the country granted outsize power by the Constitution — less populated states, which tend to be more rural — voted in broadly similar ways as large states and urban areas.

This similarity meant that the small-state bonus in the Senate and Electoral College had only a limited effect on national results. Both Democrats and Republicans benefited, and suffered, from the Constitution’s undemocratic features.

Democrats sometimes won small states like Idaho, Montana, Utah and Wyoming in the mid-20th century. And California was long a swing state: Between the Great Depression and 2000, Democratic and Republican presidential candidates won it an equal number of times. That the Constitution conferred advantages on residents of small states and disadvantages on Californians did not reliably boost either party.

In recent decades, Americans have increasingly sorted themselves along ideological lines. Liberals have flocked to large metropolitan areas, which are heavily concentrated in big states like California, while residents of smaller cities and more rural areas have become more conservative.

This combination — the Constitution’s structure and the country’s geographic sorting — has created a disconnect between public opinion and election outcomes. It has affected every branch of the federal government: the presidency, Congress and even the Supreme Court.

In the past, “the system was still antidemocratic, but it didn’t have a partisan effect,” Mr. Levitsky said. “Now it’s undemocratic and has a partisan effect. It tilts the playing field toward the Republican Party. That’s new in the 21st century.”

In presidential elections, the small-state bias is important, but it is not even the main issue. A more subtle factor — the winner-take-all nature of the Electoral College in most states — is. Candidates have never received extra credit for winning state-level landslides. But this feature did not used to matter very much, because landslides were rare in larger states, meaning that relatively few votes were “wasted,” as political scientists say.

Today, Democrats dominate a handful of large states, wasting many votes. In 2020, Mr. Biden won California by 29 percentage points; New York by 23 points; and Illinois by 17 points. Four years earlier, Hillary Clinton’s margins were similar.

This shift means that millions of voters in large metropolitan areas have moved away from the Republican Party without having any impact on presidential outcomes. That’s a central reason that both George W. Bush and Mr. Trump were able to win the presidency while losing the popular vote.

“We’re in a very different world today than when the system was designed,” said Mindy Romero, director of the Center for Inclusive Democracy at the University of

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