The Buffett Rule is an increase in the capital gains tax which is a tax that is on stock investments. The Buffett Rule would only apply to those making over a million dollars a year from investment. The problem with raising this tax is that it will both decrease investment and decrease government revenue from the tax.
Each time capital gains tax has been decreased, investment has gone up because more money could be made, and government revenue went up, because since more money could be made, more investment happened, raising government revenues. The less investment we have, the less job creation we have. The less government revenue we have, the less money we have to address the deficit, defense budget, and our ability to pay for our entitlements. Raising this tax is not what we need now.