The majority of tax payers in any flat rate system would see a dramatic increase in their actual tax rate, while the top 1% would see a tax decrease. The current progressive tax system the US has in place now works better than any other reasonable alternative.
Also, FYI, waste and fraud combined make up somewhere around 1% of the total federal budget. Some departments, like the VA, actually spend more fighting fraud than they recoup not paying fraudulent claims. The only real way to decrease the federal budget by a realistic amount is by cutting military spending, something the party in power will never do.