Um, you do realise that GDP ($13T) is quoted per annum, whereas the national debt ($10T) is quoted as an absolute figure? As long as you plan to stay around for more than one year, you get several goes at using part of the GDP to pay off the national debt. So 70% is a small percentage. That's like having a mortgage whose principal (not repayment) is 70% of your annual income (or, strictly, turnover): in other words, not something to worry about. I'm afraid it's your comparison with Ford's (annual) revenue and (annual) loss which is a non-sequitur.

But that wasn't Bitt's point. (I don't think.) He meant that it doesn't matter if the debt is historically large in absolute terms, because that might just be due to inflation. To get a better idea of whether it's worrying, one should compare it to some other indicator of the state of the economy: for instance, GDP. Again, to use a mortgage metaphor, if you're only told someone's monthly mortgage payment, you can't work out from that whether they're in financial trouble or not. You need to know their monthly income too.

Now, if the annual increase in the national debt, known as the "budget deficit", got anywhere near the GDP, that would be cause for alarm. But this year's US budget deficit (says Wikipedia) will be about $0.4T, or about 3% of GDP.

Peter