Why we have a debt ceiling, and why this trip to the brink may be different

Don't stop me, even if you've heard this one.

The debt limit is back. Congress is having another moment.

And this particular round of wrestling over the issue could carry the ugliest economic consequences yet.

The U.S. government technically ran out of money to meet its myriad obligations on Thursday. Everyone is still getting paid, for now, because the Treasury can use what it calls "extraordinary measures" to move government assets around and provide cash.

But by summer, if not sooner, cash will not be available to repay bond holders and other creditors for the loans that have already come due. Nor will there be cash to pay the military, or the millions of other federal employees and pensioners, or the beneficiaries of Social Security, Medicare, Medicaid and other entitlement programs. And that's just the payroll, leaving aside all the purchases and contract work.

That adds up to an awful lot of unpaid and unhappy people — but that's not the only reason defaulting on the debt has historically been regarded as unthinkable. If the U.S. were to default, all those unpaid creditors would be under pressure from their own creditors, setting off reverberations in credit markets worldwide.

But for those on Capitol