My only guess is, as Georgia became more conservative, so did he.
"Fiscal responsibility is unbelievable in the face of massive new spending promises. A foreign policy based on the strength of 'allies' like France is unacceptable …A strong national defense policy is just not believable coming from a candidate who built a career as an anti-war veteran, an anti-military candidate and an anti-action senator. …When will national Democrats sober up and admit that that dog won't hunt? Secular socialism, heavy taxes, big spending, weak defense, limitless lawsuits and heavy regulation – that pack of beagles hasn't caught a rabbit in the South or Midwest in years."
Haha, Tea Party Democrat.
Miller went from a fairly standard Blue Dog Democrat to Jim Inhofe with a D after his name in the space of about four years. It's very unusual for a man of Miller's age to change his political and social views so drastically. He wasn't running for reelection, so I doubt he was genuinely changing with his state. He did, however, realize that he would get much more attention and sell a lot more books if he became an Iconoclastic Archconservative Democrat, in other words a Democrat who hated Democrats. Had he just switched parties or continued to be a conservative Democrat who didn't actively undermine the party, he would have gotten a lot less attention and made a lot less money.