Blatant dictatorship – in the form of fascism, communism, or military rule – has disappeared across much of the world. Military coups and other violent seizures of power are rare. Most countries hold regular elections. Democracies still die, but by different means.

Since the end of the Cold War, most democratic breakdowns have been caused not by generals and soldiers but by elected governments themselves. Like Hugo Chávez in Venezuela, elected leaders have subverted democratic institutions in Georgia, Hungary, Nicaragua, Peru, the Philippines, Poland, Russia, Sri Lanka, Turkey and Ukraine.

Democratic backsliding today begins at the ballot box. The electoral road to breakdown is dangerously deceptive. With a classic coup d’état, as in Pinochet’s Chile, the death of a democracy is immediate and evident to all. The presidential palace burns. The president is killed, imprisoned or shipped off into exile. The constitution is suspended or scrapped.

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On the electoral road, none of these things happen. There are no tanks in the streets. Constitutions and other nominally democratic institutions remain in place. People still vote. Elected autocrats maintain a veneer of democracy while eviscerating its substance.

Many government efforts to subvert democracy are “legal”, in the sense that they are approved by the legislature or accepted by the courts. They may even be portrayed as efforts to improve democracy – making the judiciary more efficient, combating corruption or cleaning up the electoral process.

Newspapers still publish but are bought off or bullied into self-censorship. Citizens continue to criticize the government but often find themselves facing tax or other legal troubles. This sows public confusion. People do not immediately realize what is happening. Many continue to believe they are living under a democracy.

Because there is no single moment – no coup, declaration of martial law, or suspension of the constitution – in which the regime obviously “crosses the line” into dictatorship, nothing may set off society’s alarm bells. Those who denounce government abuse may be dismissed as exaggerating or crying wolf. Democracy’s erosion is, for many, almost imperceptible.

•••

How vulnerable is American democracy to this form of backsliding? The foundations of our democracy are certainly stronger than those in Venezuela, Turkey or Hungary. But are they strong enough?

Answering such a question requires stepping back from daily headlines and breaking news alerts to widen our view, drawing lessons from the experiences of other democracies around the world and throughout history.

When fear or miscalculation leads established parties to bring extremists into the mainstream, democracy is imperiled

A comparative approach reveals how elected autocrats in different parts of the world employ remarkably similar strategies to subvert democratic institutions. As these patterns become visible, the steps toward breakdown grow less ambiguous –and easier to combat. Knowing how citizens in other democracies have successfully resisted elected autocrats, or why they tragically failed to do so, is essential to those seeking to defend American democracy today.

We know that extremist demagogues emerge from time to time in all societies, even in healthy democracies. The United States has had its share of them, including Henry Ford, Huey Long, Joseph McCarthy and George Wallace.

An essential test for democracies is not whether such figures emerge but whether political leaders, and especially political parties, work to prevent them from gaining power in the first place – by keeping them off mainstream party tickets, refusing to endorse or align with them and, when necessary, making common cause with rivals in support of democratic candidates.

Isolating popular extremists requires political courage. But when fear, opportunism or miscalculation leads established parties to bring extremists into the mainstream, democracy is imperiled.

Once a would-be authoritarian makes it to power, democracies face a second critical test: will the autocratic leader subvert democratic institutions or be constrained by them?

Institutions alone are not enough to rein in elected autocrats. Constitutions must be defended – by political parties and organized citizens but also by democratic norms. Without robust norms, constitutional checks and balances do not serve as the bulwarks of democracy we imagine them to be. Institutions become political weapons, wielded forcefully by those who control them against those who do not.

This is how elected autocrats subvert democracy – packing and “weaponizing” the courts and other neutral agencies, buying off the media and the private sector (or bullying them into silence) and rewriting the rules of politics to tilt the playing field against opponents. The tragic paradox of the electoral route to authoritarianism is that democracy’s assassins use the very institutions of democracy – gradually, subtly, and even legally – to kill it.

•••

America failed the first test in November 2016, when we elected a president with a dubious allegiance to democratic norms.

Donald Trump’s surprise victory was made possible not only by public disaffection but also by the Republican party’s failure to keep an extremist demagogue within its own ranks from gaining the nomination.

By the time Obama became president, many Republicans in particular questioned the legitimacy of their Democratic rivals

How serious is the threat now? Many observers take comfort in our constitution, which was designed precisely to thwart and contain demagogues like Trump. Our Madisonian system of checks and balances has endured for more than two centuries. It survived the civil war, the great depression, the Cold War and Watergate. Surely, then, it will be able to survive Trump.

We are less certain. Historically, our system of checks and balances has worked pretty well – but not, or not entirely, because of the constitutional system designed by the founders. Democracies work best – and survive longer – where constitutions are reinforced by unwritten democratic norms.

Two basic norms have preserved America’s checks and balances in ways we have come to take for granted: mutual toleration, or the understanding that competing parties accept one another as legitimate rivals, and forbearance, or the idea that

politicians should exercise restraint in deploying their institutional prerogatives.

These two norms undergirded American democracy for most of the 20th century. Leaders of the two major parties accepted one another as legitimate and resisted the temptation to use their temporary control of institutions to maximum partisan advantage. Norms of toleration and restraint served as the soft guardrails of American democracy, helping it avoid the kind of partisan fight to the death that has destroyed democracies elsewhere in the world, including Europe in the 1930s and South America in the 1960s and 1970s.

Facebook Twitter Pinterest Joseph McCarthy speaks on the CBS news program See It Now with Edward R Murrow, April 1954. Photograph: CBS Photo Archive/Getty Images

Today, however, the guardrails of American democracy are weakening. The erosion of our democratic norms began in the 1980s and 1990s and accelerated in the 2000s. By the time Barack Obama became president, many Republicans in particular questioned the legitimacy of their Democratic rivals and had abandoned forbearance for a strategy of winning by any means necessary.

Trump may have accelerated this process, but he didn’t cause it. The challenges facing American democracy run deeper. The weakening of our democratic norms is rooted in extreme partisan polarization – one that extends beyond policy differences into an existential conflict over race and culture.

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America’s efforts to achieve racial equality as our society grows increasingly diverse have fueled an insidious reaction and intensifying polarization. And if one thing is clear from studying breakdowns throughout history, it’s that extreme polarization can kill democracies.

There are, therefore, reasons for alarm. Not only did Americans elect a demagogue in 2016, but we did so at a time when the norms that once protected our democracy were already coming unmoored.

But if other countries’ experiences teach us that that polarization can kill democracies, they also teach us that breakdown is neither inevitable nor irreversible.

Many Americans are justifiably frightened by what is happening to our country. But protecting our democracy requires more than just fright or outrage. We must be humble and bold. We must learn from other countries to see the warning signs – and recognize the false alarms. We must be aware of the fateful missteps that have wrecked other democracies. And we must see how citizens have risen to meet the great democratic crises of the past, overcoming their own deep-seated divisions to avert breakdown.

History doesn’t repeat itself. But it rhymes. The promise of history is that we can find the rhymes before it is too late.

This is an extract from How Democracies Die by Steven Levitsky and Daniel Ziblatt, professors of government at Harvard University, published in the UK by Viking and in the US by Crown

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