That's a good question. I think it's not going to be a dollar figure that does it. I think it's going to be BRICS getting enough countries to get off the USD tit. If they come up with a new currency, or go with something like China's, as the worlds reserve currency, it'll kills us monetarily and economically. China is dumping a lot of money in expanding industries in countries other than their own. Countries where labor costs are way better than ours.
It's a slow process. But if they can get enough countries on board, that can produce things they buy from us, at a cheaper cost, the USD being the worlds reserve currency will be over.