Christopher A. Preble, vice president for defense and foreign policy studies at the Cato Institute, writes in Newsweek : "In 2015, U.S. defense spending will be about $600 billion, or about 3.24 percent of GDP. The former figure would strike many Americans as sufficient, and a few would find it excessive."
"Robert Gates once said, 'If the Department of Defense can’t figure out a way to defend the United States on a budget of more than half a trillion dollars a year, then our problems are much bigger than anything that can be cured by buying a few more ships and planes.'”
"But hawks want you to focus on the latter figure, 3.24 percent: they believe that an arbitrary fixed percentage of national output should be dedicated to defense spending every year. "
The piece concludes: "America can maintain its military preeminence for decades if we reduce our military spending (or at least maintain the current caps), enact other reforms to get our fiscal house in order (including fixing entitlements) and allow our allies to better provide for their own security."