"With the race so close, investors are understandably risk-averse today," said James Hughes, chief market analyst at Alpari, a London brokerage.
Among stocks making big moves:
— Tesla Motors jumped 9 percent after the maker of rechargable electric cars said it was now producing enough of its Model S cars to generate positive cash flow. Tesla, the brainchild of PayPal billionaire and SpaceX founder Elon Musk, now has two all-electric models on the market, the $109,000 Roadster and the new Model S. The company's stock gained $2.58 to $31.50.
— Stifel Financial said it reached an agreement to buy the investment bank KBW in a $575 million deal. The boards of both companies have already signed off, but shareholders of KBW and regulators must follow suit. KBW's stock leapt $1.17 to $17.47.
— Time Warner Cable lost 6 percent, the biggest drop of any company in the S&P 500. The country's second-largest cable company posted earnings Monday morning that fell short of analysts' predictions. Time Warner reported stronger revenue across most of its businesses but lost 140,000 cable TV subscribers in three months. The company's stock fell $6.24 to $91.93.