If they REALLY want to screw US, they can do a fire sale of the treasuries that they hold to push the yield into super high to make the already flat yield curve now inversed triggering another market melt down in the US and then start the currency war all over again by devaluing the RMB yuan even further against USD to make it super cheap and USD super expensive so US exports won't sell at all widening the trade gap even more.
So now the US will be facing a crippled market and an artificially strong USD that won't allow US to sell any of the exports starting another long recession.
If the Fed is smart enough, it won't devalue the USD to help with the exports but if it's not and start to devalue USD, China can buy up US Treasuries all over again under cheap USD and with yield so high, the Treasuries price will be dirt cheap.
Of course with the economy in recession, the Fed would next be lowering interest rate then pushing the yield lower on Treasuries and China can sell US Treasuries again now that its price is higher and possibly triggering another yield curve inversing, round and round we go.
