Deteriorating Chinese-US relations most likely. It'll be interesting to see where the U.S. goes from here; Trump is under growing political pressure to be "tough on China" after attacks from Democrats. However, he can ill afford a steeply correcting stock market heading into the election. Quite the box he's in.
China orders U.S. consulate in Chengdu closed in growing spat
That probably is the likeliest cause for tomorrow’s futures.
But, the extra $600 weekly CARES payment ending may have a (small) hand in it as well? For many states, including the larger states such as CA, TX, FL, and NY, this weekend marks the end of the extra $600 payment, even though the technical end date of the program is the 31.