That is so not why treasury bonds are bought and the opposite of how they work. They are bought to be stable and value stores and some exchange rate hedging. It acknowledges supremacy sure in that they think it would be extraordinarily less likely to collapse.

They pay the money upfront for them and if the regieme change was illegitimate enough to freeze the bond it would be "free money" until a legitimate claimant comes forward. Like a neighboring city's bank refusing to turn over money from the account of Gotham after joker took over the city. That is the only securing function of it - meaning others lose it if they steal it.

So, China is a U.S. vassal state?

Civilization games taught me that vassals, when powerful enough can break their vassalage and become free again.

Perhaps that's what is happening with China. It's no longer dependent on the US in the way it was and in time, will eclipse the US as the largest superpower.

China isn't a U.S. vassal. An economic partner of convenience, maybe, the U.S. influence on China's political structure is pretty limited.