At least, it has been historically.
When US President-Elect Donald Trump takes office next week, he'll usher in a sharp shift in political tone as he succeeds Barack Obama.
Trump last year suggested in his election campaign that the US could negotiate with creditors and wouldn't need to pay the whole $13 trillion back.
The bond market has responded to the increased political risk and potential uptick in both inflation and interest rates.
A sell-off this week has seen yields on 10-year bonds, which move inversely to prices, go up to 2.60%.
The US Treasury publishes a detailed breakdown of who owns what, here's how that looks, as of October 2016: