The Dow Jones Industrial Average slipped below its 200-day moving average, joining the S&P 500 index in Monday trade. And the Nasdaq Composite Index is set to stumble below that key, long-term average, as a downdraft, driven by worries about technology stock valuations and protectionist trade policies, accelerated in Monday afternoon trade. The Dow fell as many as 730 points, or about 3%, at 23,417, with its 200-day MA at 23,422.44, according to FactSet data. Meanwhile, the Nasdaq COMP, -2.74% was trading down 3.4% at 6,824, with its 200-day moving average at 6,745.40. A breach beneath that level would signal to technical investors a broad breakdown in the market's fundamental bullish momentum. The Nasdaq stands just about 1.1% above its 200-day MA. A descent under that point would represent a breach of key technical levels for the S&P 500 index SPX, -2.23% which is threatening to close below its 200-day MA for the first time since late June of 2016. The Dow [: DJIA] also hasn't closed below its 200-day moving average since late June of 2016.