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“How could Obama choose such a day?”

That was the anguished outburst of a senior Polish officer attending a meeting of NATO chiefs of defense here when asked what he thought of the U.S. president’s cancellation last week of plans to place missile interceptors in Poland and a radar station in the Czech Republic.

The officer was referring to the fact that the announcement came on Sept. 17, the 70th anniversary of the Soviet invasion of Poland. A gesture to Russia on this date — a “brave” decision said Vladimir Putin — was the rough equivalent for the Poles of their announcing concessions to a U.S. foe on 9/11.

Poland is now one of the very few places in Europe that prefers former President...