At 09:35 ET (13:35 GMT), the Dow Jones Industrial Average fell 145 points, or 0.3%, the S&P 500 index dropped 27 points, or 0.5%, and the NASDAQ Composite slipped 108 points, or 0.6%.
Deluge of Q3 earnings 
The main focus has been the third-quarter reporting season, with about one-fifth of the S&P 500 index slated to report results this week. So far about 14% of companies in the broad index have reported results, with more than 7 out of 10 topping earnings estimates, according to FactSet.
General Motors (NYSE:GM) stock rose 5% after the auto giant reported third-quarter earnings that exceeded analyst estimates, helped by robust revenue growth and improved profitability.
Verizon (NYSE:VZ) stock fell 6% after the telecom giant reported mixed third-quarter results, with earnings slightly beating expectations but revenue falling short. It maintained its full-year guidance as it continues to see growth in wireless and broadband subscribers.
3M (NYSE:MMM) stock rose 4% after the industrial conglomerate reported better-than-expected third-quarter earnings and revenue.
RTX (NYSE:RTX) stock rose 1% after the aerospace and defense company reported third-quarter earnings that surpassed analyst estimates, and raised its full-year guidance, driven by strong demand in commercial aftermarket and defense sectors.
Electric vehicle maker Tesla (NASDAQ:TSLA) will report on Wednesday and is the biggest company reporting this week, while other Wall Street majors including AT&T (NYSE:T), International Business Machines (NYSE:IBM), Bank of America (NYSE:BAC) and Coca-Cola (NYSE:KO) are also due on Wednesday.
IMF lifts US growth forecast 
The International Monetary Fund on Tuesday raised its 2024 economic growth forecasts for the U.S., Brazil and Britain but cut them for China, Japan and the euro zone, adding that risks abound from armed conflicts, potential new trade wars and the hangover from tight monetary policy.
The IMF's latest World Economic Outlook said the shifts will leave 2024 global GDP growth unchanged from the 3.2% projected in July.
Also of interest Tuesday will be comments from FOMC member Patrick Harker.   
Four Federal Reserve policymakers on Monday backed further reductions in interest rates following the central bank's decision to cut borrowing costs by an outsized 50 basis points in September.
However, comments from these officials seemed to indicate some lingering disagreement over the pace of the drawdowns.
The US presidential election is also in focus, with Republican nominee Donald Trump seen gaining above Vice President Kamala Harris, recent polls showed, with about two weeks left to the ballot.
Crude bounces, but demand fears remain
Oil prices reversed earlier losses Tuesday, but a great deal of uncertainty clouded the global demand growth, particularly in top crude importer China.
By 09:35 ET, the Brent contract climbed 0.7% to $74.80 per barrel, while U.S. crude futures (WTI) traded 0.8% higher at $70.64 per barrel.
International Energy Agency head Fatih Birol warned on Monday that economic weakness in China will continue to stunt global oil demand in the coming years.
Birol’s comments -- made in an interview with Bloomberg -- came after both the International Energy Agency and the Organization of the Petroleum Exporting Countries recently slashed their demand growth forecasts on concerns over China.
However, tensions in the Middle East remain a support for the crude market, with traders fearful that an escalation of the conflict between Israel and both Hamas and Hezbollah could see supply from this oil-rich region severely impacted.