• The Nasdaq Composite posted its worst day since 2022.
• Global chip stocks fell on Wednesday.
• Boeing has a plan to fix the company after a string of decisions stretching back decades led to problems.

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

1. Tech sell-off

The Nasdaq Composite posted its worst day since 2022 on Wednesday, cratering 2.77% and closing below 18,000 for the first time since July 1. The broad S&P 500 also fell, losing 1.39% for the day as the rotation out of megacap technology shares continued. The Dow Jones Industrial Average, which has less exposure to the tech trade than the other two indexes, bucked the downtrend, adding 243.60 points, or 0.59% and marking its first-ever close above 41,000. This rotation away from tech comes as traders are feeling more optimistic that the Federal Reserve will cut interest rates, which should benefit small caps and companies with higher financing costs. Follow live market updates.

2. Chip dip

Global chip stocks fell sharply Wednesday with ASML, Nvidia and AMD all posting losses of more than 6%. The declines came as reports emerged that the U.S. is considering tighter export restrictions. Bloomberg reported that the Biden administration is considering enacting a rule that would clamp down on companies that export chipmaking equipment to China. Meanwhile, former President Donald Trump told Bloomberg Businessweek in an interview that he thinks that Taiwan should pay the U.S. for defense, raising doubt about if the U.S. commitment to defend Taiwan. Taiwan-listed shares of Taiwan Semiconductor Manufacturing Co. closed down 2.4% on Wednesday.

3. Softer guidance

United Airlines' profit soared more than 20% in the second quarter, helped by strong international travel. That continues a trend, as United and Delta Air Lines have stood out in the airline industry as air carriers have struggled with a surge in domestic capacity that has weighed on airfare. But United also gave a third-quarter forecast Wednesday that fell short of expectations, though it reiterated its full-year forecast. It expects to earn between $2.75 and $3.25 a share on an adjusted basis during the period, less than the $3.44 analysts polled by LSEG had estimated.

4. Can Boeing get back on track?

Boeing spent years trying to convince Wall Street, regulators, airlines and the flying public that it was focused on quality, safety and reliability after two fatal crashes of its 737 Max planes. It entered crisis mode again this year after a door plug blew out of a nearly new Boeing 737 Max 9 that was missing key bolts. Industry watchers and insiders say a string of decisions stretching back decades led to the problems. The company's leaders now say they have a plan to fix the company, with improved oversight, better safety and manufacturing procedures, and more robust training for workers. But in the meantime, the manufacturer hasn't posted an annual profit since 2018, and its stock has dropped roughly 30% so far this year as the broader market rallies. It will be back in the spotlight next week while one of the largest air shows in the world is held in the United Kingdom, though it will have a more muted presence as it focuses on pressing issues at home rather than displaying new aircraft like it has in the past.

5. Political whirlwind

President Joe Biden tested positive for Covid-19 on Wednesday and canceled his planned appearance in Las Vegas to return to Delaware, the White House said. Biden has been vaccinated and boosted, and he is experiencing "mild symptoms," White House press secretary Karine Jean-Pierre said in a statement. The news comes as Biden, 81, has repeatedly rejected calls from his fellow Democrats to withdraw from the presidential race amid concerns about his fitness to campaign. Meanwhile, former President Donald Trump's new running mate JD Vance of Ohio gave his first speech at the Republican National Convention since being selected for the position earlier this week. He blamed U.S. wage losses on China and said Trump is "America's last best hope to restore what — if lost — may never be found again."

— CNBC's Alex Harring, Arjun Kharpal, Leslie Josephs, Dan Mangan, Josephine Rozzelle, Rebecca Picciotto, Kevin Breuninger and Evelyn Cheng contributed to this report.

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