JAMES TARANTO: His Word Is Not a Bond: Why the president can’t just ignore the debt limit.

If the president spends as much as Congress has made available, and that sum falls short of what Congress has mandated be spent, he is not usurping legislative power. To the contrary, he is carrying out the will of Congress to the best of his ability.

The president would be obliged to comply with any laws governing which expenditures take priority under such circumstances, including the 14th Amendment’s mandate that servicing of existing debt is at the very top of the list. But in the absence of such laws, it seems reasonable to assume the president would have administrative discretion. (An alternative would be for judges to decide, but they really aren’t supposed to make policy.)

By contrast, if the president were to raise taxes or borrow money without congressional authorization, that would be a direct usurpation of legislative authority. Because of that, the Buchanan-Dorf proposal would be impracticable as well.

The duo want Obama to issue bonds without legal authorization. But without legal authorization, that debt would not be legally binding. Investors who bought such bonds would have no assurance of being paid back.

The U.S. is able to borrow money cheaply because of the 14th Amendment’s ironclad guarantee of repayment. U.S. bonds are the safest investment going because they will pay their promised rate of return barring a complete financial or constitutional collapse. Since the legally unauthorized Obama bonds would lack that guarantee, investors would demand a significant risk premium, assuming they were willing to buy the debt at all.

Plus, like the trillion-dollar-coin idea, it bespeaks an unseriousness about the whole thing that is unlike to instill confidence.