One thing that graph obscures (by focusing on relative amounts) is defense spending has doubled over the last decade in absolute terms. The graph makes it look like its been flat.
The following graph shows defense expenditures and investment as a percentage of U.S. GDP (blue line) and as a percentage of total federal government expenditures (red line).
The red line is exactly what Wessel shows in his graph as part of his article and that I included in my previous post, though mine goes back to 1947 and his to just 1970.
Trent argues that, although defense expenditures as a percentage of all federal government expenditures is basically flat beginning in 1997, after falling about fifteen percentage points since 1987, nominal expenditures doubled over that time. And indeed they did, increasing from $393 billion in 2001 to $824 billion in 2011, as shown in the graph below.
Wessel did not hide this fact, and actually noted that U.S. defense expenditures, which increased over the past decade to fight the wars in Iraq and Afghanistan, exceed that of the next seventeen countries combined in terms of their defense expenditures. (I've got to go back and rewatch Team America, World Police.)
But this is an important argument to have. Conservatives like to argue that defense expenditures as a percentage of total federal government expenditures have declined since WWII, other than slight increases to fight the Vietnam War, the Reagan defense buildup, Desert Storm, and the wars in Iraq and Afghanistan. At the same time, expenditures on human resources (i.e., Medicare, Medicaid, Social Security, Welfare, etc.) have increased from less than one-third of the federal government's budget to two-thirds.
I won't defend or counter the increase in spending on human resources, but I will argue that there are huge economies of scale in the provision of defense, therefore spending as a percentage of GDP should decrease as we become richer. Just because our nation grows, both in terms of population and in terms of per capita income & wealth, does not require we double the number of planes, ships, bombs, and troops we have to protect our borders. As we become richer, defense spending should naturally decline as a percentage of GDP and as a percentage of government expenditures.
Expenditures did increase over the past decade, but that was largely to fight two wars. Whether we can defend the U.S. entering into these wars or not is a different argument. But defense contractors represent a huge lobbying presence on Capitol Hill and they beg and plead for more spending on their products. Politicians are easy targets for a buck.