For the past few days, I’ve been weighing the significance of news that the US national debt now exceeds the size of our entire economy, which The Wall Street Journal reporter Richard Rubin called “crossing a once-unthinkable threshold” in a front-page story. The last time US debt crept above 100 percent of gross domestic product (GDP) was in 1946, and Americans had a World War II victory to show for it. The US stock market seems to shrug off most unsettling news these days, whether it’s continued tariff threats from the Trump administration or relentlessly rising energy prices in the face of the ongoing Iran conflict. So why should rising debt levels be any different? [...]