Stock Market Today: Dow plunges 950 points to close below 50K mark; S&P 500 skids 1.6% and Nasdaq tumbles 2% on tech rout; investors fret Iran conflict, AI and SpaceX IPO; Oracle results on tap

Shares of three big companies were doing a lot of the work to drag down the blue-chip Dow on Wednesday.
Shares of Caterpillar were off more than 5.8%, at last check, while those of Boeing and Nvidia were both almost 3% lower, according to FactSet.