US stocks: S&P 500, Nasdaq close lower, dragged by Alphabet and megacap tech; focus on Iran

Alphabet and broader megacap technology names faced investor headwinds as market participants reassess AI capital allocation efficiency. The scrutiny reflects growing concerns over whether generative AI investments will deliver sufficient returns, a critical question for MSFT and semiconductor suppliers like MU. This divergence suggests selective profit-taking in the most expensive valuations rather than systemic weakness.

The S&P 500 and Nasdaq declines were partially offset by strength in Healthcare and Industrials, as the Dow's resilience indicates rotation toward more economically cyclical and defensive sectors. This composition shift hints at underlying uncertainty about tech dominance and potential risk-off positioning ahead of macro data releases.

Falling oil prices provided a tailwind for consumer-sensitive segments, yet the Federal Reserve's hawkish stance and anticipated inflation print loom as near-term catalysts for volatility. Rate expectations remain the dominant macro variable driving asset allocation, with cautious positioning ahead of critical economic releases.

Sector implication: Technology faces valuation compression amid AI-spending skepticism, while Healthcare and Industrials benefit from relative safety appeal. Energy weakness reflects demand concerns, and broad-market correlation weakness suggests market participants are rotating tactically rather than facing demand destruction.