At best, they're choosing investments incompetently. (Chance Tether's team is equivalent to professionals at major banks?)
At worst, they're choosing investments to maximize personal gain.
Or to put it another way, what sort of company do you think is knocking on Tether's door, offering a good deal in exchange for a few billion "worth" of notes?
It ain't Coke.
At worst, they don't have any investments.
Deltec, the bank that Tether bought, has a desk specializing in zombie debt, so it's entirely possible they have loads of debt bought for pennies on the dollar, that they have through accounting/market shenanigans recognized at par as their "commercial paper".
So they don't even have to perform shenanigans.
They can just buy $1 par debt at $0.01 from Bob's Used Cars and value / declare it at $1. It's a super shady move, and would shake confidence if known, but would seem legally defensible. ("We valued it at a fair price. It turned out we were wrong and overvalued it. Oops.")
They could probably declare it at >$1 if they really wanted to, but why do hard fraud instead of easy fraud?
They are unregulated, but they're now required to publish a breakdown of their assets.
Before, they could have said "We have billions and billions in assets." Now, they're required to enumerate and value their assets, to the extent required to publish the breakdown, as part of a legal agreement.
So I guess before it could have been riskless fraud. Now, it's more risky fraud. And overvaluing assets seems like an easy way to keep the wheels turning without obviously pissing off a state AG.
As tether specifies the right to repay any redeemed tokens in securities, assuming the securities they hold actually keep their value, it seems like they'd be fine
From https://tether.to/legal/ "Tether reserves the right to delay the redemption or withdrawal of Tether Tokens if such delay is necessitated by the illiquidity or unavailability or loss of any Reserves held by Tether to back the Tether Tokens, and Tether reserves the right to redeem Tether Tokens by in-kind redemptions of securities and other assets held in the Reserves."
Of course the $60b question is, what are all the non-cash reserves they have, and how much are they worth.