AI Rally and Volatility Define Stock Run Since Trump’s Return

Donald Trump’s re-election was supposed to deliver a booming stock market. It’s done that, just not for the reasons prognosticators anticipated.

The S&P 500 Index has surged 18% since Trump’s Nov. 5 win, ending October on a six-month winning streak and at an all-time high. The run started on expectations an economic boom would follow Trump’s plan to slash taxes and regulations.

While he has largely delivered the cuts, his attempts at a wholesale re-write of US trade policies, often in fits and starts, are the market narrative he’s most responsible for. Tariff threats and walkbacks have sent a measure ...