With his jolting unexpected statement that sending Western troops to Ukraine “should not be ruled out,” President Emmanuel Macron of France has shattered a taboo, ignited debate, spread dismay among allies and forced a reckoning on Europe’s future.

For an embattled leader who loathes lazy thinking, longs for a Europe of military strength and loves the limelight, this was typical enough. It was Mr. Macron, after all, who in 2019 described NATO as suffering from “brain death” and who last year warned Europe against becoming America’s strategic “vassal.”

But bold pronouncements are one thing and patiently putting the pieces in place to attain those objectives, another. Mr. Macron has often favored provocation over preparation, even if he often has a point, as in arguing since 2017 that Europe needed to bolster its defense industry to attain greater strategic heft.

This week was no exception. By lurching forward without building consensus among allies, Mr. Macron may have done more to illustrate Western divisions and the limits of how far NATO allies are willing to go in defense of Ukraine than achieve the “strategic ambiguity” he says is needed to keep President Vladimir V. Putin of Russia guessing.

Mr. Macron’s provocation looked in part like a quest for relevance at a time when he is isolated at home and has appeared a marginal figure in the war between Israel and Hamas. France has played a central role in coordinating European Union aid to Ukraine, including a $54 billion program to support Kyiv approved this month, but its own aid contribution lags Germany, Britain and the United States.

Still, for Mr. Macron, the case for “acting differently” in Ukraine, as he put it on Monday after a meeting in Paris of leaders and officials from 27 countries, mostly European, is overwhelming.