Debt!

By 2021, the government will be spending more on interest than on all national defense. according to White House forecasts. And one year later, interest costs will exceed nondefense discretionary spending–essentially every other domestic and international government program funded annually through congressional appropriations. (The largest part of the budget is, and will remain, the mandatory spending programs of Social Security, Medicare and Medicaid. Mandatory spending is over $2 trillion and is set to double to $4 trillion by 2025.)