Quarterly taxes seems to have been the initial cover story. My guess is it ties back partially to the eurodollar carry trade. There is an unprecedented amount

Quarterly taxes seems to have been the initial cover story. My guess is it ties back partially to the eurodollar carry trade. There is an unprecedented amount of international rate and currency arbitrage going on which has pulled US dollars out of the US and could easily manifest unintended macroeconomic consequences like this. One day repo is easy for the Fed to address but if it persists then it becomes a confidence issue and people to start wonder: is this just the tip of the iceberg? If the underlying cause really is a systemic imbalance of sufficient magnitude, then who knows what else could pop up. It's more likely to signal major problems in the economies that are importing dollars (Europe in particular but also Asia) than the US itself, but a meltdown is bad for everyone; this uncertainty may be what some traders are starting to hedge against.