The Constitution states that “The validity of the public debt of the United States, authorized by law....shall not be questioned." Bruce Bartlett suggests that this trumps the debt ceiling, which means the president can simply ignore Congress if he wishes and keep spending money even after the debt ceiling has been reached. To back this up, he quotes George Washington University law professor Michael Abramowicz:
A requirement that the government not question a debt’s validity does not kick in only once the time comes for the government to make a payment on the debt. Rather, the duty not to question is a continuous one. If as a result of government actions, a debt will not be paid absent future governmental action, that debt is effectively invalid. The high level of generality recognizes that instead of referring to payment of debts, the Clause bans government action at any time that affects the validity of debt instruments.
Maybe I'm missing something here, but it strikes me that this doesn't come close to implying that the debt ceiling is unconstitutional. What it really suggests is merely that the public debt is the only untouchable part of the federal budget. The government is required to dedicate its tax revenue first to paying off any debt that's due, but once that's done the Constitution is silent. If the debt ceiling has been reached, and there's not enough money left to issue Social Security checks or buy more aircraft carriers after current debts have been paid, then Social Security checks get reduced and aircraft carriers get put on hold. The constitutional argument for ignoring the debt ceiling would only come into play if for some reason things got to the point where it literally interfered with paying off current bondholders. We're not even within light years of that happening.
I don't really like this conclusion, and I'd like to see the statutory debt ceiling go away entirely. It's an archaic budgetary vestige that makes no sense at all anymore. Still, it exists whether I like it or not, and I don't really see how it offends the Constitution as long as creditors keep getting paid.