August and the first half of September are seasonally weak periods for the stock market.  This is largely caused by the fact that Europe and New York are notorious for taking the month of August off, so trading volume tends to decline and the "B team" runs most trading desks.  The last big flash crash happened in August 2015 when many ETF investors were fleeced up to 35% intraday.  So August is a dangerous and treacherous month.  The weakness in the first half of September seems to be more related to selling to make quarterly tax payments.  Interestingly, in a Presidential election year, August and the first half of September are not too bad.  Since the Democratic National Convention (DNC) is in Chicago in August, protests may break out over Gaza and other conflicts, the DNC will be a wildcard.  Do not be surprised if the powerful Superdelagates nominate California governor Gavin Newsom to be the Democratic nominee.