The issue is that "stablecoin" doesn't mean anything legally. US regulators have collectively abdicated their responsibility to create fair rules that encourage innovation while protecting investors and creditors.
Tether publishes their reserves [1], only 4% are Bitcoin. 84% is "cash & cash equivalents & other short-term deposits", 3% is precious metals, 5.55% is "secured loans". They report $5B in net equity, ~4.2%. So basically, if their collection of assets declines in value by 4.2%, they become unable to redeem every coin. There are a _lot_ of ways for that to happen with 87% of their assets in T-bills and money market funds. If the shortest T-bill is 4 weeks to maturity, they have plenty of time to incur interest rate risk (e.g.: Silicon Valley Bank).