The Armed Forces of Ukraine are now spotting Russian planes in Belarussian airspace during attacks. It’s another sign that as President Putin’s troops are retreating, deserting, and dying, he’s preparing a northern front, gambling that he can push his lapdog in Belarus harder than the West will push back. 

Mr. Putin needs another road to the gates of Kiev, and since the capital stands just 140 miles from Belarus, he’s been nudging the nation’s president, Alexander Lukashenko, to lend a hand. Next week, when the two Soviet bloc relics meet at Minsk, it’s a safe bet they’ll plot further escalation.

This will follow the “snap combat readiness drills” Mr. Lukashenko called last week — deploying troops on Ukraine’s doorstep — and last week’s surprise meeting of defense ministers from the two nations, not to mention those Russian MiG-31Ks and Ilyushin-76 A50U in the “sky of Belarus.” 

In October, the two allies deployed integrated units within striking distance of Kiev. “The deployment,” Artyom Shraibman wrote at the Carnegie Endowment for International Peace at the time, “clearly marks the continued erosion of Belarus’s sovereignty…”

Mr. Shraibman added that “rational analysis fails to entirely reassure” that the dictators won’t make common cause, given that they “inhabit their own reality.” Keep this in mind as Minsk offers denials of belligerent intent, since before the war, the Kremlin called reports of its looming invasion “fake news.”

Rhetoric out of Belarus, like its military, is already on a war footing. Australia’s ABC News reports that the country’s authorities “have increasingly spoken of a threat of ‘terrorism’” from Kiev, and Mr. Lukashenko has warned “the president of Ukraine and the other lunatics, if they touch one meter of our territory then the Crimean Bridge [bombing] will seem to them like a walk in the park.”

The head of the George W. Bush Institute and a Vandenberg Coalition advisory board member, David Kramer, told me via email, “I think it’s unlikely Lukashenko, despite growing pressure from Moscow, will send his forces across the border to join Russia’s invasion,” however, “it can’t be ruled out entirely.”

“Such a move would be incredibly unpopular inside Belarus,” the former deputy assistant secretary of state said, “and possibly trigger renewed protests against his dictatorial rule. That said, he continues to provide a platform for Russian forces to launch attacks, so he has by no means been neutral in this war but an accomplice to Putin.” 

The best way to deter Mr. Lukashenko, who boasts about being “the last dictator of Europe,” is by being firm and clear about the consequences of more active military participation. We can’t afford a repeat of the green light given to Iraq’s Saddam Hussein in 1990 when America’s ambassador replied, “we have no opinion on the Arab-Arab conflicts” should he invade Kuwait.

President Biden offered similar muddled messages prior to Russia’s invasion, indicating that NATO might tolerate a “minor incursion.” Imagine if instead, he had told Mr. Putin that America and her allies would respond by flooding Ukraine with high-tech weapons and cash now exceeding the Russian military’s annual budget, as they have done after the fact. 

The Russian bear might have thought twice about crossing the border if he knew that such a massive trap awaited on the other side. Instead, steel teeth stamped “Made in America” clamped down on his paw only after the fact; now he can either chew it off or find another way to break free.

Mr. Lukashenko may look like a lifeline, but as the University of Michigan’s Javed Ali told Newsweek, joining the war “comes with considerable risks for the Belarusians. … Losing a few hundred troops or a couple thousand would be devastating for them,” which explains why a Chatham House poll found only 6 percent supported combat.

One thing seems certain: the Kremlin will keep prodding Minsk to expand its role in the fight, pointing to the prospect that Mr. Lukashenko would emerge as a stronger strongman after victory.