Gov. Rick Perry, a no-apologies conservative known for slashing government spending and opposing all tax increases, is about as Republican as you can get. But that wasn’t always the case. Perry spent his first six years in politics as a Democrat, in a somewhat forgotten history that is sure to be revived and scrutinized by Republican opponents if he decides to run for president. A raging liberal he was not. Elected to represent a slice of rural West Texas in the state House of Representatives in 1984, Perry, a young rancher and cotton farmer, gained an early reputation as a...