Here's a question, how do you guarantee that every USDT was backed by a dollar at origination? Say USDT holds a bond that defaults, what do they sell to offset

Here's a question, how do you guarantee that every USDT was backed by a dollar at origination? Say USDT holds a bond that defaults, what do they sell to offset the risk? Where does the 5% yield on tether even come from? This is the most plausible form of manipulation: unbacked liquidity. The only way you'll ever find out is with a bank run, and with massive yields and a hyped crypto space, it may be a while before that happens.