I think there are two points to that: the first one is the interest on that loan, which compounds and could end up to be several times the actual amount, the second is that the dollar has devalued significantly because of all this further increasing the deficit in case a part of the debt is in another currency.

If you spend 5% on top of your GDP annually (if it is that much I can't verify) and you do that for two decades you're in hock for a full years worth of GDP. If you think about GDP as your whole salary before taxes and costs then you can see how long it would take you to pay back that loan.

I hope that's all correct, I'm nowhere near an economist but that's how I read it.