The public feud between US President Donald Trump and Tesla CEO Elon Musk has turned into both a political and a Wall Street drama, raising investor concerns and exposing the vulnerability of stock markets to sharp moves in major companies.The clash, which played out mostly on social media, triggered a 14% drop in Tesla shares on Thursday, after Trump threatened to cut off government contracts to Musk’s companies. Thursday’s decline reduced Tesla’s market value by approximately $150 billion, with its weight in the S&P 500 and Nasdaq 100 at 1.6% and 2.6%, respectively.Tesla shares recovered partially on Friday, increasing about 5% by mid-day, reaching a market value of around $970 billion. Microsoft and Nvidia, both valued above $3 trillion, maintained weights of 6.9% and 6.8% in the S&P 500 as of Thursday.Despite a slight recovery on Friday, Thursday’s sharp fall weighed heavily on major US indexes, with Tesla alone accounting for nearly half the day’s declines.The company’s decline made up nearly half of the day’s losses for both the S&P 500 and the Nasdaq 100, which fell 0.5% and 0.8% respectively. The S&P 500 is widely seen as the key benchmark for the US stock market, while the tech-focused Nasdaq 100 underpins the popular Invesco QQQ ETF.“It’s a widely held stock,” said Robert Pavlik, senior portfolio manager at Dakota Wealth told Reuters. “When this big-name company that represents a sizable portion of the index sells off, it has an overall effect on the index, but it also has a psychological effect on investors,” Pavlk added.The situation highlights long-standing concerns about index concentration in a small number of large-capitalisation stocks.The “Magnificent Seven”, including Apple, Microsoft and Nvidia, collectively represented nearly one-third of the S&P 500’s total weight as of Thursday’s close. Though Tesla is the smallest among these tech and growth giants, it played a major role in driving index gains in 2023 and 2024.While 2025 started off uncertain, recent trends suggest signs of recovery.Tesla shares have dropped around 37% since mid-December, while the S&P 500 has fallen just 1% in the same period—reducing Tesla’s overall influence on the index.Tesla is included in about 10% of the roughly 4,200 ETFs, giving it wide market exposure, according to Todd Sohn, ETF and technical strategist at Strategas. Some major funds affected include the Consumer Discretionary Select Sector SPDR Fund, which fell 2.5% on Thursday, and the Roundhill Magnificent Seven ETF, which declined 2.6%.“It’s very important to know holistically what is in all your ETFs, because a lot of them are overlapping,” the analyst noted.