Last month, as the US midterm elections approached, Deutsche Bank analysts released a calculation that should have made American voters wince. It shows that the US government currently pays $1.43bn each day (yes, day) to service its public debt — 10 times more than any other G7 country (Italy is a distant second in this grim league).

This is striking, even allowing for the size of the American economy. But what is doubly thought-provoking is that this $1bn bill has materialised when interest rates are still fairly low by historical standards. And that invites a crucial question for the US Congress: what will happen to that debt, and servicing costs, if (or when) interest rates climb to a more normal level?