You have missed his point. He is saying that the US dollar is so robust that a "currency crisis" could only occur due to events that are globally devastating to

You have missed his point. He is saying that the US dollar is so robust that a "currency crisis" could only occur due to events that are globally devastating to basic infrastructure (nuclear war or what have you). I don't necessarily agree with this, but that was the argument, not that a currency crisis alone would bring down the power grid.