** S&P 500 drops 0.8% on the week as China's aggressive stance in trade war with U.S. weighs ** At first support came under fire, but then oversold levels led to a bounce ** That bounce extended, but it may have been built on sand, and may soon be washed away ** This as traders say tweets are the trump card ** Majority of sectors drop: Financials and industrials hit hardest, while defensive groups cushion the blow. Indeed, defensive shares' relative shine may grow brighter