Will the U.S. decide that Taiwan is worth defending?

Ian Buruma is the author, most recently, of The Churchill Complex: The Curse of Being Special, From Winston and FDR to Trump and Brexit. No one seems to know how the United States would react if China were to invade Taiwan. For decades, U.S. leaders did all they could to avoid this question. Then, in September of last year, President Joe Biden seemed to have ended Washington's policy of "strategic ambiguity" when he said that U.S. troops would defend the island in the event of "an unprecedented attack." But almost immediately after Mr. Biden spoke, White House officials backtracked, insisting…