With the selection of Paul Ryan as the Republican vice-presidential candidate, it is clear both political parties agree that the central issue in the coming presidential election will be the scale and scope of government involvement in the U.S. economy. There will be disagreement over what constituted “normal” levels of spending in the past and indeed over what constitutes “spending.” But there is a widespread view in both parties that it is feasible and desirable that in the future the federal government will be no larger as a share of the overall economy than it has been historically.

Unfortunately, this aspiration is unlikely to be achieved. Even preserving the amount of government functions the U.S. had before the financial crisis will require substantial increases in the share of the economy devoted to the public sector. This is the case for several structural reasons.

First, demographic change will greatly expand federal outlays unless politicians decide to degrade the level of protection traditionally provided to the elderly. Between Social Security, Medicare and Medicaid, and other smaller programs, about 32 percent of the U.S. federal budget, or about 7.7 percent of gross domestic product, is devoted to supporting those over 65. The ratio of this age group to those of working age will rise from 1:4.6 to 1:2.7 over the next generation, implying an increase in federal spending of 5.6 percentage points of GDP, if no other adjustments are made. True, as Americans’ health and life expectancy improve, it may be appropriate to revise upward the assumed retirement age. However, it will be unlikely to counteract the expected 34 percent increase over the next generation in the share of the population that will be within 15 years of estimated life expectancy.

Second, the accumulation of more debt and a return to normal interest rates will raise the share of federal spending devoted to interest payments. In 2007, before the financial crisis, federal debt held by the public was equivalent to 36.3 percent of GDP. In a very optimistic view, where recommendations such as those of the National Commission on Fiscal Responsibility and Reform (the Simpson-Bowles commission) are implemented, net debt held by the public will nearly double, to 65 percent of GDP, by 2020. This implies that the federal government’s outlays to service its debt will rise from 1.7 percent of GDP in 2007 to 3.2 percent of GDP in 2020.

Third, increases in the price of what the federal government buys relative to what the private sector buys will inevitably increase the cost of state involvement in the economy. Since the early 1980s, the price of hospital care and higher education has risen fivefold relative to the price of cars and clothing and more than a hundredfold relative to the price of televisions. Similarly the complexity and hence the cost of everything from cutting-edge scientific research to regulating banks rises faster than overall inflation. These trends reflect long-running developments in globalization and technology. They imply that if government is to continue providing the same level of these services, government spending as a share of the economy has to rise, by at least 3 percent of GDP.