But in 2017, when Mr. Haider’s Freedom Party successor, Heinz-Christian Strache, scored a similar general election result and the party was once again invited into a ruling alliance, there was little attempt to ostracize the country. President Emmanuel Macron of France and Chancellor Angela Merkel of Germany moved quickly to welcome the new Austrian government, led by the 31-year-old conservative Sebastian Kurz, who sought success by adopting much of the Freedom Party’s anti-migrant stance. The youngest leader in the expanded European Union’s 28 nations, Mr. Kurz had called for Muslim-run kindergartens to be shut down and refugees relocated to outside Europe’s borders.

The Freedom Party was gifted the foreign, interior and defense departments, and Mr. Strache — who denigrated Islam as “fascistic” and as a young man had been arrested at a torch-lit neo-Nazi procession in Germany — took control of the office of vice chancellor. The coalition agreement was fittingly announced at Kahlenberg, the site of the Battle of Vienna, which resulted in the defeat of the Ottoman Empire in 1683. Crowds gathering in the Austrian capital to oppose the new government were a fraction of those who came out nearly two decades earlier, when protests were so severe that the new cabinet could only enter and exit the inauguration ceremony through hidden underground passageways.

The story of Austria in the 21st century is, in part, the story of the wider European project. Once, the far right was anathema. Now it is routine. Born outside the mainstream, its parties now operate as a powerful political force, pushing public debate and often government policy across the continent.

How did this happen?

The far right’s rise ultimately emerges from a crisis of the political center. Politicians tasked with stabilizing the Continent after the global financial crash of 2007-08 became adept at turning the political narrative away from their own culpability. Europe’s leaders found themselves re-evaluating the benefits of historic migration into their countries — forever initiating debates on “national identity” (Nicolas Sarkozy of France), rejecting the “multiethnic” makeup of nation-states (Silvio Berlusconi of Italy) and proclaiming multiculturalism dead (Angela Merkel of Germany and David Cameron of Britain).