This post is part of Polyarchy , an independent blog produced by the political reform program at New America , a Washington think tank devoted to developing new ideas and new voices.

Over the past year, the transformation of Donald Trump from entertainingly gauche loudmouth to serious contender for the Republican presidential nomination has astounded — and frightened — America. Many things about Trump, from the brashness with which he criticizes his opponents to the unabashed pride with which he enumerates his riches, seem idiosyncratic. But he’s not the only larger-than-life xenophobe who has come to political prominence over the past years.

On the contrary, the kind of right-wing populism he represents is ascendant in virtually every liberal democracy around the world, from France to Australia, from Israel to Sweden.

Pundits and political scientists alike have spilled a lot of ink in trying to characterize the nature and the causes of this populist rise. But strangely, hardly any of them have tried to give a clear account of the actual danger that populists pose to the political system. Sure, it is unsettling — and more than a little distasteful — to see people like Trump garnering so much support. But why exactly should we be worried about them?

In my mind, there are three main reasons to worry about the rise of populists. And while the most obvious reason to worry turns out to be less important than is widely assumed, the deepest challenge posed by the populists has so far gone unnoticed.

1) Populists will win office

The most obvious reason to worry about the rise of the populists is that they might, one day, win high office.

It’s obvious why that fear looms so large. Populists like Trump pride themselves on their rhetoric against unpopular minorities, from Mexicans to Muslims. They also have little patience for the niceties of the democratic system, promising to push through their policies even if they should encounter resistance from other branches of government, like the Supreme Court. If they should actually ascend to the highest office, the damage — both to the lives of members of ethnic minorities and to the political system as a whole — would be real.

But while the prospect of Donald Trump as president of the United States — or of Marine Le Pen as president of France — is genuinely terrifying, it is easy to overstate this particular danger. In reality, it is just not that likely that they will manage to take over the government anytime soon.

Take Trump. Yes, he has consistently led polls for the Republican nomination. And, yes, he does surprisingly well in hypothetical matchups against the potential Democratic nominees, including Hillary Clinton. But to get the nomination, Trump would have to overcome stiff opposition from the Republican establishment. And should he make it to the general election, he would still have to contend with his extremely high unfavorability ratings among the general population.

While Trump may have fervent support among a significant portion of the population, he is also strongly disliked by the majority of Americans — and, as Nate Silver has pointed out, that makes it extremely hard to win the presidency.

Second, even if populists do win elections, they are likely to be hamstrung by a complex political system. In the United States, which takes the idea of checks and balances more seriously than just about any other democracy on Earth, it is especially difficult to convert a big election victory into a real change to public policies. Though the media pay outsize attention to the presidency, the office's power is actually quite limited. Unless he dismantles much of the Constitution, Donald Trump may not be able to deliver on many of his promises.

Once the populists have established themselves as a firm part of the political system, their rise becomes self-perpetuating

But even in countries like France, where the president has to contend with fewer countervailing powers, rival centers of power — from the European Union to France’s highest court, the Court de Cassation — can do a lot to soften the worst abuses of radical governments.

None of this is to say that the worst-case scenario could not come to pass. In Poland and Hungary, right-wing populists have taken over the government and done lasting damage to liberal democracy. There can be no guarantee that a similar catastrophe might not befall countries, like the United States, where democracy has been around for much longer. Disastrous as such an outcome would be, though, it remains a worst-case scenario — an extreme event that is worth taking seriously because it would be so dramatic but one that, for now, remains quite unlikely.

2) Mainstream politicians will emulate the populists

An equally important, but rather less obvious, reason to be worried about the rise of the populists is that they might influence public policy indirectly. In an attempt to keep the new competition from the far right at bay, many establishment players are starting to emulate their policies. Populists could thus undermine the rights of minorities without ever gaining office.

The recent controversy about Syrian refugees is a case in point. Donald Trump’s call to halt all Muslim immigration to the United States has been condemned by politicians across the political spectrum, from liberal Democrats to conservative Republicans. But even as they purported to be outraged by his remarks, an astounding number of mainstream Republicans echoed his views. Though they did not oppose all Muslim immigration, they did want to prioritize Christian refugees (Jeb Bush), ban all Muslim refugees from Syria (Ted Cruz), or stop taking in Syrian refugees altogether (Marco Rubio). In the wake of Trump’s attacks, more than half of the nation’s governors declared that Syrian refugees were not welcome in their states.

A similar process of "policy dispersion" from the far right to the mainstream has long been unfolding in Western Europe. Restrictive policies toward immigrants that had once been the calling card of far-right parties like the Front National or the British National Party have migrated to the mainstream. As a result, Britain’s Conservative government has capped immigration, denied scores of students visas, and restricted the ability of many British citizens to sponsor their spouses for immigration — and is now moving to throw out many people who have legally lived in the country for more than five years because they make no more than an average salary.

Similarly, François Hollande, the center-left president of France, has taken increasingly radical steps against newcomers. Only a few weeks ago, for example, he has called for naturalized French citizens to be stripped of their citizenship if they express sympathy for terrorism — an implicit distinction between "real" Frenchmen and those of foreign stock that has long been advocated by extremists like Jean-Marie Le Pen.

At first glance, the idea that mainstream politicians might start to emulate the populists is less scary than the idea that people like Trump might hold the reins of power. After all, people like David Cameron, Hollande, Bush, and Rubio have been part of the political game for a long time. It’s easy to think they will shy away from the worst abuses of power when it comes right down to it.

That may be true. Yet they are also much better placed to do real damage. It’s not just that they are more likely to amass real power. It’s also that, unlike the populists, they are able to give deeply pernicious policies a sheen of reasonableness — making it that much more likely that they are actually implemented. So if the rights of unpopular minorities in North America and Western Europe should be seriously violated, there is a good chance that it will be at the behest of the supposed establishment.

3) Establishment parties will band together, making elections meaningless

There is a third reason to worry about the populists. To the best of my knowledge, nobody has really noticed it so far, but there’s good reason to think it is the most fundamental challenge their rise poses to the political system. The concern is about the way in which the growing strength of populist parties or candidates forces traditional adversaries on the left and right to cooperate — ultimately making it impossible for voters to effect a real change in public policy without voting for extreme candidates.

In the traditional politics of most liberal democracies, the government changed hands between ideologically (reasonably) coherent parties of the center left and ideologically (reasonably) coherent parties of the center right at (reasonably) regular intervals. When a center-left government became unpopular, it would lose some key swing voters at the next election, thus allowing the center-right government to form a government. Once the new center-right government fell from grace, power reverted back to the center left.

To form a stable government that excludes the populists, historical adversaries had no choice but to join forces

Each handover of power resulted in ideologically motivated, if moderate, adjustments to public policy. (The story has long been a bit more complicated in the United States, mostly because of the role played by Southern Democrats.)

This system had a number of important attributes. Even though it might, at any one point, be unclear who exactly would be in the next government, the range of possibilities was limited; the country’s future politics thus seemed predictable to a reasonable degree. Even more importantly, voters were able to correct their country’s political direction without having to shake the political system to its core; if they grew dissatisfied with a center-left government, they could vote it out by returning the center right to power, and vice versa.

In many countries, the rise of the populists has destroyed this system over the past two decades. Once populists captured a significant share of the vote, neither traditional center-left parties nor traditional center-right parties were able to muster a majority of their own. To form a stable government that excludes the populists, historical adversaries had no choice but to join forces. The result has been the rise of so-called "grand coalitions" — governments formed by the big establishment parties that have opposed each other for many decades — in many parts of Europe, from Germany to Italy.

The rise of these grand coalitions has three worrying consequences for the political system. The first is that the populists’ old battle cry, according to which all mainstream politicians are basically the same, has turned into a self-fulfilling prophecy: Forced to form joint governments, politicians from parties that had long claimed to be mortal enemies really did have to overcome their ideological divides.

The second problem is that it becomes very difficult for voters to force out a government when it becomes unpopular. Instead of being governed by an ideologically coherent government with a small majority, they are faced with a centrist blob with a commanding majority. Under these circumstances, elections are very unlikely to result in policy change — and thus lose much of their meaning.

The third and final problem is that the formation of a grand coalition makes it very easy for populists to keep gaining in strength. Since they are the only real opposition to the government, voters who are desperate for political change have little choice but to vote for them. Once the populists have established themselves as a firm part of the political system, their rise becomes self-perpetuating.

The United States might look like an obvious exception to this development. After all, ideological polarization between the two most powerful parties has steadily increased rather than decreased in America. What’s more, while plenty of populists have been elected to office over the past two decades, Democrats and especially Republicans have proven very effective at keeping them under the nominal wing of their parties.

But a closer look at Washington reveals that many of the dynamics that are openly on display in Europe are going on under the hood in the United States. Yes, the ideological distance between moderate Democrats and moderate Republicans has increased. But so has the gulf between moderate Republicans and Tea Partiers. And, yes, the two big parties have not been forced to form a joint government. But because of the Tea Party’s intransigence, the only way to pass vitally important bills, like this year’s budget deal, is for Democrats and moderate Republicans to make common cause. For the foreseeable future, Democrats and Republicans thus have the same unenviable choice faced by their European counterparts: Band together to pass bills — or brace for legislative paralysis.

In politics, it is easy to be mesmerized by the most dramatic scenario. I’m hardly immune to this. The thought of a President Trump is enough to send cold shivers down my spine. But in an odd way, we are making life too easy for ourselves when we fixate on this worst-case scenario. The most serious threat posed by the populists is not some dystopian future under President Trump — a future that, as of yet, remains very unlikely. Rather, it is the very real ways in which populists are already poisoning our public policies and making our elections largely meaningless.