VLADIMIR PUTIN has spent much of his two decades in power attempting to restore Moscow’s rule over former republics of the Soviet Union. For the most part, he has failed. Though he has applied economic pressure, organized electoral fraud, mounted propaganda campaigns and cyberwars, and, in the cases of Georgia and Ukraine, resorted to military invasion, he has regained only a few fragments of territory outside Russia’s borders, while alienating nations that used to be close friends.

Yet Mr. Putin is undeterred. He has now mounted a new effort to subjugate Belarus, a country of 10 million wedged between Russia, the Baltic states and Poland. His aim is to force Belarusan President Alexsander Lukashenko to finally implement a 20-year-old agreement that would merge the two countries, essentially turning Belarus into a province. Mr. Lukashenko is resisting, saying he does not want to be “the last president of Belarus.” Though he is anything but an attractive partner for the West, his attempt to save his country deserves support.

To be sure, Mr. Lukashenko, and the West, have been here before. The wily autocrat has avoided Mr. Putin’s demands for concessions on sovereignty, and Western pressure for the liberalization of his regime, by maneuvering back and forth between the two. Along the way, he has missed some opportunities. After promising fair presidential elections in 2006 and 2010, Mr. Lukashenko rigged them, then brutally suppressed protests. The result was U.S. and European Union sanctions; the United States has not had an ambassador in Minsk since 2008.

That may now change, thanks to Mr. Putin’s latest push. The Russian leader has discontinued deliveries of subsidized oil on which the Belarusan economy heavily depends, while demanding implementation of the long-dormant union treaty. In a meeting Friday, Mr. Putin again rejected Mr. Lukashenko’s appeals for oil and gas discounts. If that position holds, the Belarusan economy could be severely damaged: A fifth of its exports consist of refined products from cheap Russian oil.

Mr. Lukashenko has made a show of resisting Russian pressure, buying a tanker load of oil from Norway. And Secretary of State Mike Pompeo has made a show of helping him, visiting Minsk on Feb. 1 — the first State Department chief to do so since 1993. Mr. Pompeo promised that the Trump administration would dispatch a new ambassador to Belarus, and he assured Mr. Lukashenko that “our energy producers stand ready to deliver 100 percent of the oil you need at competitive prices.”

No doubt Mr. Pompeo took some satisfaction in that offer at a time when Russia is keeping Venezuela’s oil industry afloat despite U.S. sanctions. But even if delivered, U.S. petroleum would not rescue Belarus’s refineries. Instead, Mr. Lukashenko might have to choose between knuckling under to Mr. Putin — or at least taking steps in that direction — and subjecting his economy to the shock therapy that would be necessary to free it from Russia. If he chooses the latter course, the United States and the E.U. should do what they can to ease the pain, while continuing to press for improvements in human rights.

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