ABBEVILLE, France — For President Emmanuel Macron of France, it has been Europe or bust from the beginning.

Since his election two years ago, he has fashioned himself as the leader of Europe, laying out a grand vision of deeper integration. He has tried to stoke passion in a skeptical populace with an open letter in newspapers to “the citizens of Europe.” He has warned urgently of a “European civil war” that threatens the continent’s values.

In the process, Mr. Macron has become the far right’s favorite whipping boy, the trim-suited stand-in for the so-called faceless bureaucrats in Brussels, his name spat with contempt by populists from Hungary to Italy and even in France.

Mr. Macron’s vision now faces its most critical test in elections for the European Parliament, starting on Thursday. Polls in France show his party trailing Marine Le Pen’s far-right Rassemblement National, or National Rally, the party that used to be called the National Front.