A charitable read of President Macron’s Ukraine policy might describe it as spotty. His early dismissals of British-American intelligence warning of an impending Russian invasion were succeeded by a series of futile dialogues with President Putin, punctured by repeated calls against “humiliating Russia.” As a result, French military support to Kyiv ranks about 14th among allies.

Now, the French president is calling for Western boots-on-the-ground in Ukraine. Let us see if, in his newfound resolve, Mr. Macron grounds his efforts in coherent strategy, avoiding well-meaning yet possibly misguided policy gambits. His sudden rise as a leading Western champion of Ukraine finds its cause in three factors.

First, a brush with reality. His prior efforts to engage Mr. Putin reflected his interactions with such other strongmen as President el Sisi of Egypt and Saudi Arabia’s Crown Prince Mohammed bin Salman. With varied results, he has over the years been able to sway them towards, if not fully his worldview, some of his positions. Yet Mr. Putin deceived him and remained impervious to his diplomatic advances as Russia’s military upped its aggression.

Second, President Macron likely sees championing Ukraine as a tactic to frustrate the National Rally in the June European polls and its potential victory in the 2027 French presidential race. The rightist RN leads Mr. Macron on every matter of voter concern. Except one: Ukraine. For now, most French appear to favor support for Kyiv.

The RN’s Marine Le Pen, who is expected to mount her fourth presidential bid, has opposed new weapon shipments to Ukraine and pushed for lifting sanctions against Russia. What better than to paint her as Russia’s fifth column? Yet, crucially and thirdly, Mr. Macron seems to believe his time has come.

Even before he assumed the presidency, Mr. Macron advocated for an overhaul of European institutions and principles. Such drive is largely rooted in his ideology. Yet it stems, too, from his belief in his own grandeur and hopes of legacy. With Germany’s ostensible abdication of European leadership and America’s perceived retreat, Mr. Macron sees the moment as ripe. Initially, such legacy was to be forged “not against, but with Russia.”

Twenty months later, Monsieur Macron appears to have realized that closer ties with Eastern Europe, which he once largely disregarded, might best advance his aims. Yet what, exactly, are they? “No option should be ruled out,” Mr. Macron said of allied North Atlantic Treaty troops in Ukraine. “No limits” and “no red lines.” The strategic imperative of defeating Russia is clear. Yet one must also consider Moscow’s red lines.

It is an unpopular yet vital consideration. The prevailing view is that aggression should be met with aggression. “It’s about Putin being afraid,” the Polish foreign minister, Radosław Sikorski, said. But would he be? The uneasy reality is that since Russian tanks rolled into Ukraine the West has largely miscalculated President Putin. He has circumvented Western sanctions, boosted Russia’s military-industrial base, and persists seemingly undeterred.

Would allied troop deployments to Ukraine shift his calculus? If there were to be no red lines for President Macron, why would there be for President Putin? The Russian president has also not yet exhausted all the tools in his arsenal. He could, as I have previously cautioned, unleash waves of African Islamists on Europe. The Wagner Group remains active across Western Africa and the Sahel. In January, it rebranded as “Africa Corps.”

What of another front? In its efforts to undermine the West, Russia is united with Communist China, Iran, and North Korea — Ukraine is one part of a larger puzzle. Hamas’s assault on Israel opened a Middle Eastern front that might yet expand. What of the Korean Peninsula, the Indo-Pacific, or Europe itself? President Biden has rightly dismissed the notion of NATO membership for Kyiv while it remains in active combat.

Under Article V, such a move would likely expand the conflict. Would Mr. Putin regard Western troops stationed in Ukraine for what Mr. Macron has proposed as “noncombat roles” the same way? Might this escalate the nuclear risk? Any ruminations about Western troops in Ukraine necessitate careful assessments of at least such scenarios. “Peace through strength” succeeds only when “strength” is integrated into a holistic security strategy.

So far, President Macron does not appear to have one. He might, then, consider tempering his bellicosity. For it was also in pursuit of personal glory and domestic triumph that another Frenchman, Napoléon III,  in 1870 declared war on Prussia. A more dismal outcome could scarcely have been fathomed.