The arbitrageurs buy USDT at a discount and redeem it, pocketing the difference. This creates a buying pressure, that tends to bring the price back up to $1.

The arbitrageurs buy USDT at a discount and redeem it, pocketing the difference. This creates a buying pressure, that tends to bring the price back up to $1. Buying USDT and hoping that it repegs is not arbitrage. If tether fails to redeem USDT arbitrage will stop and nothing will prevent USDT from falling more.