• All major indexes closed lower Tuesday.
• Tesla and Alphabet reported earnings after the bell.
• Previously owned homes sales fell in June compared to May.

Here are five key things investors need to know to start the trading day:

1. In the red

All major indexes closed lower for Tuesday's trading session. The S&P 500 moved marginally lower, falling 0.16% to close at 5,555.74. This comes after the broad market index saw its best day in a little more than a month. The Nasdaq Composite saw the smallest percentage loss out of all the indexes, moving 0.06% lower to close at 17,997.35. For the Dow Jones Industrial Average, the index declined 0.14% to close out the session at 40,358.09. Following results for the second quarter that missed expectations, UPS shares fell 12% for its worst day on record. While General Motors' earnings beat expectations, shares ticked 6.4% lower as the company delayed EV plans. Follow live market updates.

2. Taking a hit

There were some misses after the bell Tuesday. Tesla posted second-quarter earnings that missed Wall Street's expectations, with automotive sales falling for the second period in a row. The electric vehicle maker reported adjusted earnings of 52 cents per share compared with the 62 cents per share analysts surveyed by LSEG expected. The company did beat on revenue, however, posting $25.50 billion compared with the consensus estimate of $24.77 billion. Alphabet took a hit in YouTube advertising revenue, as the segment generated $8.66 billion, below the $8.93 billion analysts were expecting, according to StreetAccount. Alphabet topped the Street's earnings and revenue expectations, posting earnings of $1.89 per share compared with the $1.84 per share expected. The company's revenue came in at $84.74 billion, above the $84.19 billion consensus estimate.

3. Slumping sales

It appears we may be heading into a buyer's market. Compared with May, previously owned home sales dropped 5.4% in June to 3.89 million units on a seasonally adjusted, annualized basis. That's according to the National Association of Realtors. Sales were also 5.4% lower than a year earlier. This marks the slowest sales pace since December. On the inventory side, June saw a 23.4% increase compared with the same time last year and 1.32 million units were available – the highest supply since May 2020. The average time a home sat on the market was 22 days, which is a four-day increase from a year ago. Meanwhile, prices were still higher, as the median price of an existing home sold in June was $426,900. This is a 4.1% increase compared to the year-ago period as well as an all-time high for the second month in a row.

4. Secret's Out

The director of the U.S. Secret Service officially stepped down. On Tuesday, Kimberly Cheatle resigned after the attempted assassination of former President Donald Trump at a Pennsylvania rally earlier in July that left one attendee dead and two others critically injured. This comes a day after Cheatle testified before the House Oversight and Accountability Committee during a hearing on the Secret Service's actions leading up to the Pennsylvania rally. The director refused to answer many questions about the Secret Service's actions, angering lawmakers of the House committee. In a letter to the agency's staff, Cheatle wrote, "In light of recent events, it is with a heavy heart that I have made the difficult decision to step down as your Director."

5. Facing scrutiny

The U.S. Department of Transportation is investigating Delta Air Lines' widespread flight disruptions and customer service failures in the aftermath of an IT outage on Friday. The airline saw thousands of flight cancellations and the DOT said Delta did not uphold commitments to its passengers. The agency added that the investigation will develop with the processing of a "high volume" of customer complaints. In response, Delta said in an emailed statement that it's fully cooperating. "Across our operation, Delta teams are working tirelessly to care for and make it right for customers impacted by delays and cancellations as we work to restore the reliable, on-time service they have come to expect from Delta," the carrier said.

— CNBC's Samantha Subin, Alex Harring, Ece Yildirim, Michael Wayland, Lora Kolodny, Jennifer Elias, Diana Olick, Dan Mangan, Rebecca Picciotto, Justine Fisher and Leslie Josephs contributed to this report.

— Follow broader market action like a pro on CNBC Pro.