Written by: Craig Erlam | Oanda Jitters have well and truly set in and equity markets are suffering the consequences as investors head for safety in numbers.Every time investors find the strength to pick themselves up off the floor, the trade war delivers another blow and knocks them down again. This morning that came in the form of reports that China is threatening retaliation against Trump's tariffs that are due to come into force on 1 September.Europe was trading in the green ahead of the report, paring losses after a rough session on Wednesday, but that didn't last long and now we're once again seeing some pretty heavy losses. US futures aren't faring much better, which doesn't bode well for Wall Street which suffered quite a backlash a day ago.I guess this report also answers the question of whether China viewed the decision to delay half of the tariff hikes until mid-December as being conciliatory in any way or just an act of self-preservation, given the importance of the holiday season in the US. The market reaction also clearly highlights that investors are concerned about the economic impact of the trade war, regardless of Trump's assertion that the Fed is the problem.