Russia-appointed administrators in towns, villages and cities like Kherson in Ukraine’s south are setting the stage for a vote as early as September that the Kremlin will present as a popular desire in the region to become part of Russia. They are recruiting pro-Russia locals for new “election commissions” and promoting to Ukrainian civilians the putative benefits of joining their country; they are even reportedly printing the ballots already.

Any referendum would be totally illegitimate, Ukrainian and Western officials say, but it would carry ominous consequences. Analysts both in Moscow and Ukraine expect that it would serve as a prelude to Mr. Putin’s officially declaring the conquered area to be Russian territory, protected by Russian nuclear weapons — making future attempts by Kyiv to drive out Russian forces potentially much more costly…

The prospect of another annexation has affected the military timetable as well, putting pressure on Kyiv to try a risky counteroffensive sooner, rather than waiting for more long-range Western weapons to arrive that would raise the chances of success.

“Carrying out a referendum is not hard at all,” Vladimir Konstantinov, the speaker of the Russian-imposed Crimean Parliament, said in a phone interview this week. “They will ask: ‘Take us under your guardianship, under your development, under your security.’”