Less than a day after President Trump celebrated “record highs” on Wall Street, U.S. markets delivered a reminder of how quickly the mood can turn.

What happened
– The S&P 500 plunged as much as 3.8% on Thursday, wiping out Wednesday’s post‑election rally and putting market circuit breakers back in focus. At the time of reporting the index had not yet hit a market-wide halt, but it would need to fall another roughly 3.2 percentage points from the intraday drop to trigger the first automatic pause.
– Wednesday’s strength had followed sweeping Democratic midterm wins: the S&P gained 1.6%—its biggest one‑day rise in three months—after investors cheered the election outcome. Trump had posted on Truth Social that “Stock Market…