The main obstacle standing between Barack Obama and the White House was distilled into five words by a local television correspondent in South Charleston, W.Va., earlier this month. Prefacing a question about the challenges of winning over white, blue-collar voters, the reporter offered this observation: “They think you are un-American,” he said. Such questions, asked by reporters and plainly on the minds of voters in Appalachia and elsewhere, are the fruits of an unprecedented, subterranean e-mail campaign. What began as a demonstrably false attempt to cast Obama as a Muslim has now metastasized into something far more threatening to the...