Because it represents foreigners investing in United States and that generates rates of return that effectively can generate that growth.

其实这和外国人在美国投资的道理是一样的,投资带来的收益，是由美国来埋单的,因而，实际上也同样导致了美国债务的增长。

斯坦福公开课 - 经济学课程节选

Now, assuming that we trust the government-- I think the U.S. Government has never defaulted on its debt-- we'd take that as a riskless return.

假设我们信任政府-,假设美国政府从未拖欠债务-,可以把它当作无风险回报。

耶鲁公开课 - 金融市场课程节选

You take total household debt and total federal debt and combine them, and you got a kind of national indebtedness 168% that's about 168 percent of GDP.

将美国所有家庭债务总额,加上联邦政府债务总额，得出整个美国的债务状况,整个债务量竟是GDP的。

斯坦福公开课 - 经济学课程节选