US stocks fell sharply on Thursday as two separate pressures hit markets at the same time: a consumer inflation reading that climbed to a three-year high and fresh geopolitical tension after President Donald Trump issued a threat against Iran.

The S&P 500 and the Dow Jones Industrial Average both dropped noticeably, while the Nasdaq Composite fell around 1%, dragged lower by a broad sell-off in semiconductor stocks.

Inflation Runs Hot

US consumer price inflation topped 4% in May, reaching its highest level in three years. That number matters because the Federal Reserve uses inflation data as its primary guide for setting interest rates. When inflation runs above the Fed's 2% target by this margin, it raises the probability that the central bank will raise borrowing costs rather than cut them.

Higher interest rates are generally bad for stocks. They make future corporate earnings worth less in today's money, increase borrowing costs for companies, and pull investors toward safer assets like bonds. Technology and growth stocks, which are valued heavily on future profits, tend to take the biggest hit, which explains the pressure on the Nasdaq in particular.

The chip sector amplified the Nasdaq's decline. Semiconductor companies are especially sensitive to rate expectations because they carry high valuations relative to current earnings, and because their global supply chains are exposed to geopolitical disruption.

Iran Threat Adds Pressure

Separately, President Trump issued a threat directed at Iran, adding a layer of geopolitical risk that markets dislike. While the specific nature of the threat was not detailed in official disclosures, any escalation involving Iran tends to move oil prices and raise uncertainty across risk assets broadly. Investors typically respond by pulling back from equities and moving toward safe-haven assets such as gold, the US dollar, or Treasury bonds.

The combination of a domestic inflation shock and an international security risk arriving on the same day created a difficult environment for buyers. Neither factor on its own would necessarily cause a sharp sell-off, but together they reinforced a cautious mood.

For the Fed, the May inflation print complicates an already difficult balancing act. Markets had been pricing in the possibility of rate cuts later in the year, partly on the assumption that inflation was cooling. A reading above 4% challenges that assumption directly and may force traders to reprice the timeline for any easing. Fed funds futures, which track market expectations for the central bank's policy rate, are likely to shift toward fewer cuts or a later start date following this data.

For equity investors, the path forward depends on whether this inflation reading is seen as a one-month spike or the start of a renewed upward trend. If subsequent data confirms that inflation is re-accelerating, the case for rate cuts weakens further and stock valuations face sustained pressure. If May turns out to be an outlier, markets may recover quickly.

What to watch: the Federal Reserve's next policy meeting and any statement from Chair Jerome Powell responding to the May CPI data. Also watch oil prices and any further developments in US-Iran relations, as an escalation there could add a second round of selling pressure through energy costs and broader risk aversion.