BRUSSELS — This was supposed to be the year Europe put its house in order. It would finally ratify a deal with Britain on its departure from the bloc. The French president, Emmanuel Macron, with his grand plans to revitalize the Continent, would succeed Chancellor Angela Merkel of Germany as the union’s de facto leader. Democratic backsliding in Hungary and Poland would be curbed. Populism would be contained.

If only.

Turmoil is now business as usual. The difference as another angry year comes to an end is that the European Union no longer has a strong leader to guide it through the crises that keep upending its agenda. Ms. Merkel played that role but is now a lame duck, her voice quieter on European affairs. Mr. Macron is confronted with violent protests and a widespread domestic crisis of his own making in France, his presidency at risk.

The political upheaval was obvious on Tuesday with the latest turns in the great British psychodrama of Brexit. Prime Minister Theresa May spent much of the day flying to European capitals for emergency meetings, like a penitent on some dire continental pilgrimage, desperately seeking new help from the Europeans to resurrect a Brexit deal that she had pulled from a parliamentary vote to prevent certain defeat.

“This is a moment of truth, a moment of recognition that things are more difficult than they seemed a year ago,” said Pierre Vimont, a former French ambassador and former director of the European foreign service.