From the Washington Times dated October 25, 2012. All bolded emphasis is mine.
The central problem is that America is the bank of the world. What this means, simply, is that the dollar is the world’s currency (often termed the “reserve currency”). Throughout the world, nearly all traded goods, oil, major commodities, , etc., are denominated in dollars. The world needs dollars, and the U.S. provides them and provides confidence that the dollar is the “safest” currency in the world. Countries get dollars by trading with us on attractive terms, which enables Americans to live very well. Countries support this system and cover their risk by investing in dollars through T-bill auctions and other mechanisms, which enables us to run budget deficits — up to a point.
The central issue is confidence in America, and the world is losing confidence quickly. At a certain point, soon, the United States will reach a level of deficit spending and debt at which the countries of the world will lose faith in America and begin to withdraw their . Many leading economists and bankers think another trillion dollars or so may do it. A run on the bank will start suddenly, build quickly and snowball.