Brazil, China and Russia dumping U.S. currency
As I've mentioned before, the U.S. currency has been under threat of massive deflation if it reverts from it's reserve currency status. In the past, the threat has been from the rise of PetroEuros due to the diversified European political decision making and it's oil dependence. This Clark hypothesis saw oil as the main trigger to a change in security of the U.S. currency through OPEC adopting multiple oil trading currencies instead of relying on the U.S. dollar.
Instead, it is the collapse in U.S. credit as part of the global financial crisis which has lead China, Russia and Brazil to trade out U.S. currency.