It's also possible that Miller simply feels slighted. Miller is an immensely proud man and acutely sensitive to signs of condescension toward his rural heritage. He grew up in a tiny north Georgia mountain town, and his book is filled with paeans to rural life and such proudly folksy asides as "I own a fiddle that supposedly belonged to Zeb Vance" (a former mountaineer and North Carolina governor in the 1860s). Upon leaving the governorship in 1998 Miller said that one of his greatest regrets was that he never challenged "someone at the Atlanta newspapers to duel over their never-ending bigotry toward rural mountain people." More than once, he has taken to the Senate floor to launch a tirade against someone for stereotyping "hillbillies"—including one stemwinder aimed at CBS last year for its proposed laugh-at-white-trash reality show, The Real Beverly Hillbillies.
A National Party No More makes it clear Miller sees today's Democrats as snooty elitists—and he resents them. "The biggest problem with the party leadership is that they know nothing about the modern South," he writes. "They still see it as a land of magnolias and mint juleps, with the pointy-headed KKK lurking in the background, waiting to burn a cross or lynch blacks and Jews."
But there has been no long-term Democratic abandonment of the South. Clinton and Gore were both Southerners, and so is John Edwards. The party tends to be far more timid on issues like guns and gay rights than its base would like—precisely for fear of alienating Southern and Midwestern rural voters. It's the South that has abandoned Democrats, as Republicans take advantage of social issues to win over voters whose economic interests are better aligned with the Democratic Party. In the 1990s Miller warned Democrats not to let the GOP beat them at this game. Today Miller is one of its best practitioners.
So why doesn't Miller just switch parties? He says that he was born a Democrat and considers his party label "like a birthmark." More likely he realizes that once he becomes a Republican he stops being interesting. As a Democrat, Miller is an entertaining man-bites-dog story, and a minor celebrity in GOP circles. As a Republican he's just another partisan hack.