A U.S. sovereign debt crisis is a remote possibility, but in our increasingly fragile system it could be triggered by a number of financial catastrophes—​from a chaotic break-up of the Euro system to something as adventitious as a serious earthquake in California. The most likely source of a U.S. sovereign debt crisis, however, is a failure of the U.S. political system to address the growth of the major entitlement programs—Social Security, Medicare and Medicaid. That possibility is discussed in this paper.