There are three examples in recent history of supply side economic policies and how this pro-growth macro-economic theory has jump started severe recessions and led to years of economic growth. The proof of its effectiveness can be seen even with all the smoke and mirrors put up by big government liberals.
Supply side economists believe that if you put the capital that already exists back into the hands of the taxpayer and decrease government regulation that it will result in greater economic activity, more business investment, and more risk taking by entrepreneurs. This will then lead to a growing economy with more tax revenue and more job opportunities with ever increasing wages.