That’s the title of a timely paper by MIT researcher Dr. Cindy Williams [.pdf]. The summary points:
1. The United States currently devotes about 4.7 percent of gross domestic product (GDP) to national defense and another 1.5 percent to broader security efforts, including international affairs, homeland security, veterans’ affairs, and intelligence.
2. What share of GDP will be affordable for security over the long term depends on a variety of factors, including:
– Public perceptions of the security threat;
– The degree of debt-induced fiscal and economic risk policy makers are willing to run;
– The level of taxation the public is willing to bear;
– Whether and how much the costs of federal entitlement programs, particularly Medicare and Medicaid, can be reined in; and
– How much money is devoted to running the rest of the federal government.
3. Putting federal budgets on a sustainable path will require shifting about six percent of GDP into revenues or out of spending, relative to their likely current course, according to the Congressional Budget Office.
4. Depending on how that shift is distributed among taxation, entitlement spending, defense spending, and nondefense discretionary spending, an affordable long-term level for national defense will be between 1.6 percent and 2.6 percent of GDP.
5. An affordable long-term level of total security spending might thus be between 2.1 percent and 3.4 percent of GDP.