S&P 500 is following a giant descending triangle, even though on 04.18.18 it has not touched the triangle. Overall the market is bearish short term , despite being in the earnings season. In a bullish market some neutral and positive earnings report would have been interpreted as bullish .
Increasing treasury yields may be partly to blame. As investors are buying more bonds for safety the yield increases and we passed the 3.0% yield today which carries a psychological importance as well (e.g 8 years ago it was 3.9%).
Adding political and global uncertainties to this created a market that is much more easily spooked compared to Jan'18. See VIX
The critical resistance for the S&P 500 index is at 2580. If we break lower the chances are that mutual fund managers technical analysts are going to advice : "sell, sell, sell".