My biggest concern is after quite a lot of years in a bull market - and one long sustained run since late 2011 - the S&P 500 is having trouble at the 2.618 level: The ES1! contract shows during the last eight months was much heavier on the sell months than the buy months:
I suspect the market is undergoing distribution. I don't know what could spur this market for much longer. I'm pessimistic now.