By Noah Barkin
BERLIN (Reuters) - Back in May, when Donald's Trump's victory in the U.S. presidential election seemed the remotest of possibilities, a senior European official took to Twitter before a G7 summit in Tokyo to warn of a "horror scenario".
Imagine, mused the official, if instead of Barack Obama, Francois Hollande, David Cameron and Matteo Renzi, next year's meeting of the club of rich nations included Trump, Marine Le Pen, Boris Johnson and Beppe Grillo.
A month after Martin Selmayr, the head of European Commission President Jean-Claude Juncker's cabinet made the comment, Britain shocked the world by voting to leave the European Union. Cameron stepped down as prime minister and Johnson - the former London mayor who helped swing Britons behind Brexit - became foreign minister.
Now, with Trump's triumph over his Democratic rival Hillary Clinton, the populist tsunami that seemed outlandish a few months ago is becoming reality, and the consequences for Europe's own political landscape are potentially huge.
In 2017, voters in the Netherlands, France and Germany - and possibly in Italy and Britain too - will vote in elections that could be colored by the triumphs of Trump and Brexit, and the toxic politics that drove those campaigns.
The lessons will not be lost on continental Europe's populist parties, who hailed Trump's victory on Wednesday as a body blow for the political mainstream.
"Politics will never be the same," said Geert Wilders of the far-right Dutch Freedom Party. "What happened in America can happen in Europe and the Netherlands as well."
French National Front founder Jean-Marie Le Pen was similarly ebullient. "Today the United States, tomorrow France," Le Pen, the father of the party's leader Marine Le Pen, tweeted.
Daniela Schwarzer, director of research at the German Council on Foreign Relations (DGAP), said Trump's bare-fisted tactics against his opponents and the media provided a model for populist European parties that have exercised comparative restraint on a continent that still remembers World War Two.
"The broken taboos, the extent of political conflict, the aggression that we've seen from Trump, this can widen the scope of what becomes thinkable in our own political culture," Schwarzer said.
Early next month, Austrians will vote in a presidential election that could see Norbert Hofer of the Freedom Party become the first far-right head of state to be freely elected in western Europe since 1945.
On the same day, a constitutional reform referendum on which Prime Minister Renzi has staked his future could upset the political order in Italy, pushing Grillo's left-wing 5-Star movement closer to the reins of power.
"An epoch has gone up in flames," Grillo said. "The real demagogues are the press, intellectuals, who are anchored to a world that no longer exists."
Right-wing nationalists are already running governments in Poland and Hungary. In western Europe, the likelihood of a Trump figure taking power seems remote for now.
In Europe's parliamentary democracies, traditional parties from the right and left have set aside historical rivalries, banding together to keep out the populists.
But the lesson from the Brexit vote is that parties do not have to be in government to shape the political debate, said Tina Fordham, chief global political analyst at Citi. She cited the anti-EU UK Independence Party which has just one seat in the Westminster parliament.
"UKIP did poorly in the last election but had a huge amount influence over the political dynamic in Britain," Fordham said. "The combination of the Brexit campaign and Trump have absolutely changed the way campaigns are run."
UKIP leader Nigel Farage hailed Trump's victory on Wednesday as a "supersized Brexit".
As new political movements emerge, traditional parties will find it increasingly difficult to form coalitions and hold them together.
In Spain, incumbent Mariano Rajoy was returned to power last week but only after two inconclusive elections in which voters fled his conservatives and their traditional rival on the left, the Socialists, for two new parties, Podemos and Ciudadanos.
After 10 months of political limbo, Rajoy finds himself atop a minority government that is expected to struggle to pass laws, implement reforms and plug holes in Spain's public finances.
The virus of political fragility could spread next year from Spain to the Netherlands, where Wilders's Freedom Party is neck-and-neck in opinion polls with Prime Minister Mark Rutte's liberals.
For Rutte to stay in power after the election in March, he may be forced to consider novel, less-stable coalition options with an array of smaller parties, including the Greens.
In France, which has a presidential system, the chances of Marine Le Pen, leader of the far-right National Front, emerging victorious are seen as slim.
The odds-on favorite to win the presidential election next spring is Alain Juppe, a 71-year-old centrist with extensive experience in government who has tapped into a yearning for responsible leadership after a decade of disappointment from Francois Hollande and Nicolas Sarkozy.
But in a sign of Le Pen's strength, polls show she will win more support than any other politician in the first round of the election. Even if she loses the second round run-off, as polls suggest, her performance is likely to be seen as a watershed moment for continental Europe's far-right.
It could give her a powerful platform from which to fight the reforms that Juppe and his conservative rivals for the presidency are promising.
In Germany, where voters go to the polls next autumn, far-right parties have struggled to gain a foothold in the post-war era because of the dark history of the Nazis, but that too is changing.
Just three years old, the anti-immigrant Alternative for Germany (AfD), has become a force at the national level, unsettling Chancellor Angela Merkel's conservatives, who have been punished in a series of regional votes because of her welcoming policy toward refugees.
Merkel could announce as early as next month that she plans to run for a fourth term, and if she does run, current polls suggest she would win.
But she would do so as a diminished figure in a country that is perhaps more divided than at any time in the post-war era. Even Merkel's conservative sister party, the Bavarian Christian Social Union, has refused to endorse her.
(Additional reporting by Crispian Balmer in Rome, Anthony Deutsch in Amsterdam; editing by David Stamp)