The Dow Industrial Average, down 369 points at the lows of Wednesday's session, posted its worst decline since November 2011.
It's a broad decline for the markets. All 10 S&P sectors are down more than 1 percent. If losses hold, it will be the first time since Dec. 8, 2011, that all 10 sectors end with declines of more than 1 percent.
And if the Dow closes below 13,000, it will be the first time since Aug. 2, 2012.
Downbeat comments from ECB President Mario Draghi regarding Germany's outlook, the U.S. presidential election, and Apple's slide are all partly responsible for the sell-off.