Economics
Krugman is usually wrong, but even a stopped clock gives the right time twice a day. The national debt is a scare tactic to block spending on things the working class wants while still allowing almost unlimited spending on the things the capitalist class wants.
Here’s what the national debt is: All the US dollars the federal government has created out of thin air by spending minus all the US dollars it has destroyed by taxing. That’s it. If the federal government had no debt, then there wouldn’t be any money, because federal spending is where the US dollars come from in the first place†.
†Actually much of the money comes from US private banks, which the Federal government has deputized to create money out of thin air in the form of loans. But for every loan “credit” dollar a bank creates, it also creates one loan “debt” dollar, so in the end, once the principal is paid off, those dollars cancel each other out.