Looking at the monthly chart, SPX is testing 8 year long orange trendline once again. There is a very high probability that bears will start shorting SPX. Both RSI and MACD indicate bearish divergence.
To me this last few days of trading seems to be liquidating shorts and people who entered the shorts at 3400 are trying to cover their shares. Usually under this scenario, one red day will be very devastating. In short term, let's see if 3400 will act as a support.