The just-concluded Italian election is a watershed moment in the remarkable rise of populism.

The past few years have amply demonstrated that populists in North America and Western Europe can occasionally cobble together surprising majorities. Now, the Italian case shows that they have astounding longevity—and can become absolutely dominant in a country that had long been considered a consolidated (if admittedly chaotic) democracy.

Italy’s political landscape is so baroque that it’s pointless to explain the ins and outs of the country’s many rival parties and movements. But Fonderie Creative, a group of Italian graphic designers, has done a very nice job of summarizing the most important movements in advance of the election.

With The Simpsons as a helpful cheat sheet, here’s what you need to know about yesterday’s results:

• Krusty the Clown, aka the Movimento Cinque Stelle (Five Star Movement), came out as the strongest political party, taking about one-third of the vote nationwide. Radically critical of all existing political institutions, the Five Star Movement has recently started to deploy more anti-immigrant rhetoric, has received sizeable support from Russian sources in the past, and is seemingly run by a shadowy PR firm. Although its leaders pledged that they would stay in opposition, they are now demanding to take a role in the government.

• Snake Jailbird, aka the Lega Nord (Northern League), took about 18 percent of the vote. Founded as a separatist party that advocated for the independence of the country’s affluent north, the League has, under the leadership of Matteo Salvini, transformed itself into a hypernationalist and virulently xenophobic party in the mold of France’s National Front. When a former candidate for the party shot six African migrants in the city of Macerata in the middle of the campaign, Salvini pointedly refused to condemn him.

• Mr. Burns, aka former Prime Minister Silvio Berlusconi’s Forza Italia, took 14 percent of the vote. Berlusconi, a self-made billionaire who dominated Italian politics from 1994 until his ignominious fall from power in 2011, is simultaneously an ideological moderate whose economic and social policies are largely within the bounds of ordinary Italian politics and an institutional radical who has weakened the Italian judiciary to keep himself out of jail.

In case you’ve been counting, Krusty, Jailbird, and Mr. Burns have nearly two-thirds of the vote between them. Poor Springfield.

How this sorry cast of characters is actually going to rule Italy is anybody’s guess. The Five Star Movement’s short record of government at the local and regional level has been an unmitigated disaster, and they lack realistic coalition partners. Before the election, many commentators assumed that a “center-right” coalition between Berlusconi’s Forza Italia and Salvini’s League might rule the country. The center-left Partito Democratico (Democratic Party) could conceivably lend this government informal support. But because Salvini has taken more votes than Berlusconi, and would therefore lead such a government, this would essentially amount to a Social Democratic party helping to make a far-right extremist the prime minister of the country—which would set a terrible precedent for other parts of Europe, and be all but certain to destroy the party. (There’s also another horror scenario: a coalition between the most extreme and euroskeptic parties, Five Stars and the League; but at least for now, Salvini seems to have ruled this possibility out.)

The most likely outcome, then, is protracted negotiations that lead either to an unstable and short-lived government or to new elections. Italy has always been chaotic; now, it is to all intents and purposes “ungovernable,” as a daily newspaper headline read Monday.

This, then, is the kind of politics you get when trust in liberal democracy hits rock bottom, mutually hostile anti-system parties proliferate, and ideologically coherent coalitions become impossible. Welcome to 21st-century Europe.

The consequences for Italy are likely to be tragic. The country is not only unspeakably charming and beautiful; it also retains real economic strengths, including a vibrant manufacturing sector in the north. But its history of corruption and over-regulation has, for many decades, been sapping its strength. While Italy had a higher per capita GDP than the United Kingdom as recently as the early 1990s, it has barely experienced any growth in the past decades and now lags far behind.

During an unusual period of reasonable leadership by the center-left Democratic Party since 2013, the country has been finally starting to recover. This year, Italy’s GDP was forecast to grow by 1.5 percent. Now, investors are going to think twice about pouring more money into the country, and the possibility of a crisis of confidence that would make Italy’s high public debt unsustainable once again looms on the horizon.

This, then, is the kind of politics you get when trust in liberal democracy hits rock bottom.

The most depressing manifestation of the twin crisis of omnipresent corruption and sluggish growth has been a widespread feeling of hopelessness among young Italians. Youth unemployment is very high. Unskilled and semi-skilled jobs are largely given to the children of friends and relatives. Even highly qualified doctors or lawyers need to go to humiliating lengths to procure employment, and often fail. Every year, tens of thousands of the most ambitious and talented young Italians leave the country.

This dire situation makes it perfectly understandable that so many young people around the country have decided to vote for the Five Star Movement, which has best captured their anger at the status quo and their cynicism about a rigged political and economic system. But the dysfunction that Krusty the Clown will bring to Rome is also likely to deepen their malaise. As in so many other countries, populists in Italy have thrived by railing against failings that are all too real but are likely to implement solutions that only serve to aggravate them.

It is tempting to think of the rise of populism as a self-correcting mechanism. On this account of the current situation, these parties rise because traditional elites have failed to deal with public frustrations. Their entry into politics either pushes traditional parties to get their act together or empowers newcomers who can do better. Over time, the system stabilizes.

But the Italian case suggests that the rise of populism may, instead, be self-radicalizing. While it is true that populists rise because traditional political elites have failed to deal with public frustrations, their success makes it even more difficult for moderate parties to deal with them. Instead of helping to address the root causes of public anger, populists make them more acute, and voters grow even more agitated. Over time, the system becomes even more chaotic.

There is also another important lesson the world can take from the Italian election, as the important (and as yet unpublished) work on the pathways of populism by Jordan Kyle makes clear: When Berlusconi fell from grace in 2011, Italy seemed to turn away from populism. But in truth, the cancer just metastasized. Now, an even more aggressive form of it is ravishing different parts of the body politic all at once.

Similarly, it is tempting to think that things will go back to normal if Donald Trump leaves the White House in 2020. But as the experiences of Italy and many other countries around the world show, it is not enough to beat an authoritarian populist to free a country from the threat of strongman rule. Anybody who wants to save liberal democracy has to resolve the deep reasons for public frustration about the political system, not just combat its most immediate and glaring manifestation.