From the same article: “As of April 30, 2018, debt held by the public was $15.3 trillion and intragovernmental holdings were $5.7 trillion, for a total or "National Debt" of $21 trillion.[5] Debt held by the public was approximately 77% of GDP in 2017, ranked 43rd highest out of 207 countries.[6] The Congressional Budget Office forecast in April 2018 that the ratio will rise to nearly 100% by 2028, perhaps higher if current policies are extended beyond their scheduled expiration date.[7] As of December 2017, $6.3 trillion or approximately 45% of the debt held by the public was owned by foreign investors, the largest being China (about $1.18 trillion) then Japan (about $1.06 trillion).[8]” of the 6 trillion held by foreigners China has a sixth of it. Followed closely by japan. The point is that if an entity owning 1/12th of your debt decided to start selling it that entities’ borrowing costs would rise a lot which could lead to inflation. Inflation hurts our ability to buy aka purchasing power.