The web platform was named for a revered French populist philosopher and created by an Italian internet entrepreneur to transform common grievances into proposals and activists into political candidates. When Italy's deputy prime minister offered the populist 5-Star Movement's Rousseau platform to France's yellow vest protesters, he took a step too far for French President Emmanuel Macron. The French leader recalled France's ambassador to Italy for a week in the sharpest diplomatic dispute between the two allies since World War II. The sharing of the Rousseau technology marks the most brazen attempt to date to internationalize Europe's populist movements. It is a harbinger of the upcoming European Parliament elections in May, in which populist euroskeptics could win an unprecedented one-third of the seats, under current projections . This could well cause a collapse of the mainstream group, which up to now has held the largest voting bloc in Parliament. However, the EU elections will also be a test of how far populist parties, which tend to be virulently nationalistic, can unite over borders and across the political spectrum. In Italy alone, the government's two populist ruling parties, the 5-Star Movement and the League, compete at least as much as they cooperate. 'These parties are against Europe, but they are using Europe and the pan-European space to create a political debate,' said Alberto Alemanno, an Italian analyst. At their most basic level, populists on both the right and the left pit the common people against the elite, the entrenched political class. Technology has helped them advance . The 5-Star Movement used the Rousseau portal to let activists click their way to choosing candidates and policies, much as Spain's upstart Podemos party used Reddit to energize online debate beginning five years ago and still uses online referendums. France's populist yellow vest protesters have yet to come up with a common online space, with proliferating Facebook groups and YouTube channels that have a varied outpouring of demands. If ideology and organization can trump geography, populist parties in Europe could form a bloc capable of weakening or even paralyzing the EU legislature, if projections released this week by the parliament hold. 'We must reject the financiers who see themselves as demigods. Reject the Brussels bureaucrats representing their interests and reject the fake civil society activists,' Hungarian President Viktor Orban said in his state of the nation address earlier this month. On Friday, 5-Star leader Luigi Di Maio announced a new grouping of populist movements from across Europe, bringing together a far-right Polish party led by a former rock musician and a free-market Finnish party founded by a businessman-turned-reality TV star. Notably absent were nationalists, leaving open the question of how much sway the new alliance could have without expanding further. Getting the far-left France Unbowed to vote in tandem with populist Orban's Fidesz party seems a big hurdle. Italy's government, split between the two populist groups, is largely an unhappy marriage of convenience, with the 5-Star Movement and the League diverging at least as much as they agree. But among the yellow vests, known in French as the 'gilets jaunes,' ultra-right and ultra-left have marched together in hopes of bringing down the government. 'Here is the beauty of it: They are both the left and the right. It is a populist thing,' political strategist Steve Bannon told France's l'Express magazine in an interview published just after Macron recalled the ambassador. Bannon has created a foundation in Brussels to strike at the heart of the European Union. Europe's populists on the right — France's Marine Le Pen, Hungary's Orban, Italy's Matteo Salvini — haven't exactly embraced him, but nor have they pushed away the American who many credit with propelling Donald Trump into the White House. Bannon been largely ignored by the populist far-left. The European Parliament elections are actually a four-day series of national elections held May 23-26 across Europe that decide the makeup of the legislature. Members make Europe-wide law, decide international agreements, and — crucially — can censure EU countries for violating core values such as an independent judiciary and upholding the rights of minorities and migrants. But even if they can unite on the issues that brought them to power, the anti-EU populists may run into trouble with voters. Across the board, trust in the European Union is higher than trust in national governments, according to the latest Eurobarometer poll taken in November 2018 — just as the yellow vest protests were taking root. The poll found 42 percent of Europeans trusted the EU, compared with 35 percent who trusted their own national governments or parliaments. So even as Orban and Italy's populists position themselves squarely against the pro-EU Macron, they are keenly aware that their own citizens have little desire to overthrow the EU, although they list immigration as their prime concern. And Macron himself is something of an upstart — he vanquished France's two mainstream parties in the first round of France's 2017 presidential election and Le Pen in the second. France's two centrist mainstream parties, the Socialists and the Republicans, have since sunk in popularity. They held their seats in Brussels but are widely expected to further their political collapse in May's EU vote. However, voters may also use the European Parliament vote to protest. Under current projections, the extremes on the right and left are set to gain at the expense of the mainstream. 'Those voters who vote for the more radical parties just to express their frustration with Europe, they face a risk of voting for solutions that they wouldn't normally agree to,' said Pawel Zerka, one of the authors of a study last week by the pro-EU European Council for Foreign Relations that said euroskeptics stand to gain the most in the EU vote. Even some who are pro-EU think an alliance among euroskeptic populists is not necessarily bad for the parliament. For Alemanno, the Italian analyst based in Paris whose last name translates loosely as 'the German,' it's ironic proof that the European idea is strong and durable, as populists come together in a European union of their own. 'In a way, I look at the yellow vests from an Italian perspective. I see the 5-Star Movement 10 years ago,' he said. The kind of interference that Macron found so intolerable from the 5-Stars will become more common and even welcome, he said. In the short term, he added, the EU parliament and by extension the EU itself may well be nearly ungovernable. Le Pen has already shifted away from her longstanding position of abandoning the EU and the euro, the common currency that is used by 19 EU nations. She renamed the nationalist party founded by her father, and Bannon made a surprise appearance at a major rally last year. And, she says, her brand of populist nationalism is no longer the exception. 'We can legitimately envision today to change Europe from inside, to modify the very nature of the European Union,' Le Pen said, 'because we consider ourselves powerful enough.' ___ This story corrects the date of Orban's speech to earlier this month.