The OP wants to short USDT against USD. He is wanting to effectively bet on USDT not being backed by USD on a 1:1 basis.
It's a bit more complicated than that. Despite Bitfinex adding a small Polish bank to its arsenal, Tether has made no announcements regarding redemption of Tether. If people could redeem at 1:1 easily, I don't think the USDT/USD rate would fluctuate as much as it does.
The market is very illiquid (thin order books), creating trade opportunities. It also gets pushed around by 1) demand for altcoins not offered on Kraken and 2) Bitfinex/Tether FUD. For instance, we have a 15% range on the daily chart:
![](https://ip.bitcointalk.org/?u=https%3A%2F%2Fi.imgur.com%2FoYcxR6a.png&t=665&c=1d-FGGzBWqU5Mw)
This is my general take: During altcoin pumps, the USDT price spikes above $1 as traders use USDT to disperse to different altcoin exchanges. Historically, anything in the $1.03-1.07 range is a good short. It tends to hold ~ $1. That spike down to $.90 was due to the Tether hack. I wouldn't entirely discount further opportunities with all the FUD floating around.
USDT can't really go above 1:1 in value against the USD. If the conspiracy theory brigade succeeds in pushing the price far enough down I'd definitely be a buyer of discounted USDT.
It can go higher, as explained above. At the height of altcoin season earlier this year (May-June), it was holding above $1 for weeks at a time. One thing about buying "discounted" USDT: If it dumps heavily, just make sure you know why before you buy.
For example, if Bitfinex or Tether is facing trouble with law enforcement or regulators, I probably wouldn't want to be holding USDT. I don't like to trade it myself. It's one of those get in/get out kind of assets to me.