Tether got few attestations from an unknown company a few times, but they have also been caught red handed by NYAG for moving funds a day before attestation snapshot is taken, and moved it the day after.
For the uninitiated, attestation verifies a single point in time, so it's easy to game it. And this is something tether has done.
"Pump and dump" refers to promoting some investment by other means, usually spreading some false news.
I beg to differ. The Securities and Exchanges Act of 1934 criminalizes all sorts of things that are deemed market manipulation, and inflating the price of a security by false trading, i.e. selling it to yourself or a conspirator, is one of the very things it was created to prohibit.
Which auditors? The only ones I know of quit before making a statement (which is a very bad sign).
Now they claim to be backed by cash and cash equivalents, namely a lot of "commercial paper" (short term debt obligations), which is widely believed to be in Chinese markets.
For some reason though, they won't reveal exactly what it is they hold. It could be that they think the market will not react kindly to the kind of assets they hold, or that they entered some kind of weird agreement no to reveal them.
I highly doubt they're not backed by assets whose face value adds up to the total UST distribution, because multiple auditors have said they were fully backed. But it is possibly that some of these assets are junk that won't (or have a high risk not to) redeem at face value.
Even in very bad scenarios, UST could fall to 0.8$ if 20% of Tether's asset default (and they burned through profits). Problematic but not quite such as a risk as it going to zero, which is why people still hold it.