It was a positive day for US equities until Trump blew it up at 10:30 am ET with a tweet threatening new tariffs on China because of rare earth controls. Details have been light since then but the market isn't waiting for details. The last few months have been a smashing success for bulls and at this point, asset managers might not want to risk ruining the year. That makes it a fairly easy decision to take profits and the Nasdaq fell more than 3%.In an ominous sign, US stock markets closed on the lows.Closing changes:Nasdaq -3.5%S&P 500 -2.7%DJIA -1.9%Russell 2000 -2.6%Toronto TSX Comp -1.2%On the week:Nasdaq -2.4%S&P 500 -2.5%DJIA -2.7%Russell 2000 -2.9%Toronto TSX Comp -1.9%Some big losers:TSLA -5.0%BIDU ADRs -8%QCOM -7.3%AMZN -4.95%META -3.9%OXY -5.1%FDX -5.0%AMD -7.8%NVDA -4.7% This article was written by Adam Button at investinglive.com.