The CME's margin raises always effect the stock market in a harsh manner. This whole latest S&P dump started on May 1 when they went after oil and silver. The effects last longer on the S&P too. Attempts at price controls and interventions make it very difficult for companies to do business. And pulling liquidity is pulling liquidity.
I looked over the margin requirements for paper gold and silver. The bankers are not effected by this margin change at all. The hedger margins are already way below the spec margins with initial and maint being the same. Only the specs maint will go up. The margin raise is really not that bad, but since it is across the board on everything, it will probably be an effective temporary price control in PMs. The COT report doesn't show many traders to shake out here.
I do find it odd that there was no raid on Friday before this news release came out. Usually they orchestrate this kind of thing. Gold and silver, being money, will probably take the lead after the shake out again. I think the S&P will probably stay weak.