In July, the S&P 500 rose 1.9 percent, the Dow added 2.5 percent and the Nasdaq gained 3.4 percent.
Apple Inc, which is expected to report quarterly results after the market close on Tuesday, dipped 0.51 percent.
Investors have been counting on earnings to support high valuations for equities.
S&P 500 earnings are expected on average to have grown 10.8 percent in the second quarter, according to Thomson Reuters I/B/E/S.
“The market in the last week has become jittery,” said Dennis Dick, head of markets structure, proprietary trader at Bright Trading LLC in Las Vegas. “Money managers are looking to take profits and for any excuse to do so.”
The Dow Jones Industrial Average rose 0.28 percent to end at 21,891.12 points and the S&P 500 lost 0.07 percent to 2,470.3. The Nasdaq Composite dropped 0.42 percent to 6,348.12.
Just four of the 11 major S&P sectors rose, with the financial index’s 0.62 percent rise leading the gainers.
Tesla dropped 3.46 percent after Chief Executive Elon Musk warned that the electric carmaker would face “manufacturing hell” as it ramps up production of its new mass-market Model 3 sedan.
Snap fell 1.01 percent as some investors were allowed for the first time to sell shares following the Snapchat owner’s March initial public offer.
Discovery Communications dropped 8.21 percent after it said it would buy Scripps Networks Interactive for $11.9 billion.
Charter Communications Inc rose 5.85 percent to a record high after a source said Japan’s SoftBank Group Corp was considering an acquisition offer.
About 6.3 billion shares changed hands in U.S. exchanges, above the 6.0-billion average over the last 20 sessions.
(Additional reporting by Sinead Carew and Kimberly Chin in New York; Editing by Nick Zieminski and James Dalgleish)