Colorado has an income tax, yet Colorado also has a big budget shortfall thanks to the recession, proving that not even an income tax can assure a state will avoid fiscal crises. But that's not the most important lesson of Colorado's budget crunch. The truth is Colorado's $1 billion shortfall would have been far worse if the state hadn't finally placed a firm limit on the growth of spending a few years ago. The Taxpayer Bill of Rights (TABOR) in Colorado's constitution limits spending growth to the rate of inflation plus population growth. Revenue above that TABOR limit is...