You are attempting to blame the engine for a flat tire. Supply side economics doesn't have a damn thing to do with our current economic woes, or wealth/earnings inequality.
Over the last fifty years, the United States, along with all of the countries of the world, have been moving from localized economies to a world economy. This shift has caused disruptions in national economies, as capital shifts with the constantly changing world markets.
Labor suffers because labor, for the most part is not mobile, and is forced to deal with the local conditions, while capital can move freely and rapidly, anywhere in the world to take advantage of favorable economic trends.
Attempting to fight this globalization is futile and counter productive to a local economy. We must accept the inevitable, and learn to prosper in the new environment. Government can do little to help, and most of the politicians efforts have caused more harm than good.