Some laws are too dangerous to be allowed to remain on the books. Take, for example, the US debt ceiling. It is the legislative equivalent of a nuclear bomb aimed by the US at itself, with the rest of the world within its blast radius. What must never be used should not exist. Regardless of the outcome of the current negotiations, the law needs to be repealed. Orderly government cannot be pursued under so destructive a threat. It is quite different from a partial government shutdown. Albeit foolish and unjust, that is just about manageable. Failure to lift the debt ceiling is not.

The imbroglio over the ceiling does have a darkly amusing side. Many will recall Republican insistence that “uncertainty” was thwarting economic recovery. Yet it is difficult to imagine policies better designed to create maximum uncertainty than a possible default by the world’s most important debtor. Asked about the consequences of a failure to reach a deal on the ceiling, Jamie Dimon, chief executive of JPMorgan Chase, responded: “You don’t want to know.” But we must seek to know; the results would be calamitous.

Why is the debt ceiling too dangerous to use? This question has two answers.