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.
Zimbabwe option, anyone? Or the alternative of tax rates exceeding the peak from World War II — forever.
Have a nice day.