Why did he do it? Why conjure up unquiet ghosts? Why now? Vietnam is not only, as President Bush rather flatly put it, “a complex and painful subject” for Americans. The V-word is lodged in folk memory as an unwinnable war that America should never have fought, that wasted blood and treasure, and that, most woundingly, bitterly split the nation. Vietnam, even today, is a powerful political toxin. Probably the only American politician who can talk about Vietnam without risk is the war hero John McCain. John Kerry tried the “veteran who wants out of Iraq” line in the 2004...