This has been a point of contention between the left and the right for years. No sensible person argues the sky's the limit on America's capacity to borrow. Pile on enough debt fast enough, and you will do serious damage to the economy. But are we close to that tipping point, as conservatives and the GOP argue? Or are we very far away from it, as progressives (like me) insist?

To definitively answer this question, we need data. Specifically, we need a real-world example of America pushing its borrowing capacity to the max. As it turns out, we've got one: World War II.