By David Cay Johnston
The author is a Reuters columnist. The opinions expressed are his own.

If the U.S. government voluntarily defaults, how are you going to get that tax refund? Or get paid for the work your company did for Uncle Sam?

While a last-minute agreement to raise the debt ceiling could still be reached, the risk of default as early as Tuesday is causing jitters in global financial markets and anxiety among people who depend on Social Security to eat.

Without an increase in the debt ceiling, the president is faced with an irresolvable conflict between faithfully executing those laws passed by Congress requiring payments for services and benefits and his inability to borrow more.

As William A. Galston of the Brookings Institution neatly put it: “We would be in uncharted legal territory and uncharted constitutional territory.”