Jeffrey Hummel says its likely:
Predicting an ultimate Treasury default is somewhat empty unless I can also say something about its timing. The financial structure of the U.S. government currently has two nominal firewalls. The first, between Treasury debt and unfunded liabilities, is provided by the trust funds of Social Security, Medicare, and other, smaller federal insurance programs. These give investors the illusion that the shaky fiscal status of social insurance has no direct effect on the government's formal debt. But according to the latest intermediate projections of the trustees, the Hospital Insurance (HI-Medicare Part A) trust fund will be out of money in 2017, whereas the Social Security (OASDI) trust funds will be empty by 2037.5 Although other parts of Medicare are already funded from general revenues, when HI and OASDI need to dip into general revenues, the first firewall is gone. If investors respond by requiring a risk premium on Treasuries, the unwinding could move very fast, much like the sudden collapse of the Soviet Union. Politicians will be unable to react. Obviously, this scenario is pure speculation, but I believe it offers some insight into the potential time frame.
The second financial firewall is between U.S. currency and government debt. It is not literally impossible that the Federal Reserve could unleash the Zimbabwe option and repudiate the national debt indirectly through hyperinflation, rather than have the Treasury repudiate it directly. But my guess is that, faced with the alternatives of seeing both the dollar and the debt become worthless or defaulting on the debt while saving the dollar, the U.S. government will choose the latter. Treasury securities are second-order claims to central-bank-issued dollars. Although both may be ultimately backed by the power of taxation, that in no way prevents government from discriminating between the priority of the claims. After the American Revolution, the United States repudiated its paper money and yet successfully honored its debt (in gold). It is true that fiat money, as opposed to a gold standard, makes it harder to separate the fate of a government's money from that of its debt. But Russia in 1998 is just one recent example of a government choosing partial debt repudiation over a complete collapse of its fiat currency.