American "decline" is the foreign-policy equivalent of homelessness: The media only take note of it when a Republican is in the White House. Broadly speaking, declinists divide between those who merely accept America's supposed diminishment as a fact of life, and those who celebrate it as long overdue. As for the causes of decline, however, they tend to agree: declining (relative) economic muscle, due in large part to the rise of China; an overextended military bogged down needlessly in Iraq and endlessly in Afghanistan; the declining value of America's "brand" on account of Bush administration policies on detention, pre-emption, terrorism, global warming -- you name it.

Yet each of these assumptions collapses on a moment's inspection. In his 2006 book "Überpower," German writer Josef Joffe makes the following back-of-the-envelope calculation: "Assume that the Chinese economy keeps growing indefinitely at a rate of seven percent, the average of the past decade (for which history knows of no example). . . . At that rate, China's GDP would double every decade, reaching parity with today's United States ($12 trillion) in thirty years. But the U.S. economy is not frozen into immobility. By then, the United States, growing at its long-term rate of 2.5 percent, would stand at $25 trillion."

Now take military expenditures. Yesterday, the administration released its budget proposal for 2009, which includes $515.4 billion for the regular defense budget. In inflation-adjusted dollars, this would be the largest defense appropriation since World War II. Yet it amounts to about 4% of GDP, as compared to 14% during the Korean War, 9.5% during the Vietnam War and 6% in the Reagan administration. Throw in the Iraq and Afghanistan supplementals, and total projected defense spending is still only 4.5% of GDP -- an easily afforded sum even by Prof. Kennedy's terms.

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