President Obama's decision Thursday to abandon the so-called Third Site of missile defense systems in Poland and the Czech Republic already is generating fierce debate and causing great consternation. The decision is a slap to America's Polish and Czech allies, who had braved Russian intimidation in agreeing to host the sites. But Mr. Obama's step also will have profound implications on many of America's other alliances, especially in Asia.

One major problem is the flimsy strategic rationale offered...