The troops started to move into the country in late July, with the exercises scheduled for mid-September. Both the Russian and Belarussian authorities have vowed publicly that the troops will return home after the exercise.
Over the years, as Mr. Lukashenko has sought to demonstrate his independence, he has periodically picked fights with Russia’s president, Vladimir V. Putin — stage-managed affairs that have been quickly patched up in highly public displays of Slavic brotherhood.
As Moscow’s relations with the West have plunged to levels last seen during Soviet times, however, Mr. Lukashenko’s balancing act has grown increasingly untenable. The time may be approaching when he will have to choose between the two camps, a decision that carries decided risks.
An overt move to embrace the West could provoke a reaction from the Kremlin, as happened in Ukraine after the ouster of President Viktor F. Yanukovych. The West almost certainly would not oppose such a move militarily.
But a complete embrace of Russia would collapse Belarus’s sovereignty and could renew the street demonstrations that erupted this year among a population already seething over declining living standards.
Most analysts assume that Mr. Lukashenko, if forced to choose, will throw his lot in with his patrons in Moscow.
“Belarus can build many bridges to the West, but it cannot cross any of them,” said Artyom Shraibman, sitting in the modern newsroom of Tut.by, the country’s leading independent news website, where he is a political editor. “The European vector is just a way to balance the relationship with Russia.”