The Standard & Poor's 500 index fell 1.4% this week, its first weekly loss in a month, as US President Donald Trump issued an "economic D-Day" warning to Iran.

The S&P 500 ended Friday's session at 7,674.37. This is the first time the market benchmark has posted a weekly decline since the five days that ended on July 24. The index has gained 2.5% in August and 12% in 2026.

Trump threatened the "most crushing economic operation" on Iran, while also warning of consequences for countries that support or conduct business with Iran. Iran's foreign minister responded by saying the campaign was bound to fail.

Also this week, the US Treasury decided to boost repurchases of long-dated government debt to $4 billion per operation from September.

Utilities had the largest percentage loss this week, falling 3.6%, followed by a 3.4% drop in industrials and a 3.2% decline in technology. Communication services, financials and consumer staples shed at least 1% each while real estate and consumer discretionary also edged lower.

NRG Energy (NRG) and Vistra (VST) were the hardest-hit stocks in the utilities sector, falling 10% and 8%, respectively.

Airline stocks United Airline (UAL) and Southwest Airlines (LUV) were among the top decliners in industrials, sliding 9.7% and 8.8%, respectively.

In the technology sector, shares of CrowdStrike (CRWD) fell 12%.

The company faces high expectations heading into Q2 results and the annual Fal.Con conference, BofA Securities said in a note to clients. Investors may need a meaningful net new annual recurring revenue beat to justify elevated expectations, the report said. Also, CrowdStrike's global chief technology officer, Elia Zaitsev, stepped down to launch an early-stage venture capital fund focused on cybersecurity.

On the upside, health care climbed 4.3%, followed by a 2.5% increase in energy and a 2.3% gain in materials.

Moderna was the best performer in health care as well as the overall S&P 500, more than doubling on the week as the company and Merck said a late-stage trial of an experimental skin cancer treatment they are jointly developing yielded positive topline results. Merck's shares rose 12%.

Economic data next week will include the July Personal Consumption Expenditures (PCE) index and the second estimate of Q2 gross domestic product. Other data will include July consumer spending, new home sales, durable goods and wholesale inventories.