As the Iran war drags on, are Trump’s tactics to regulate markets working?

As the Iran war intensifies, President Donald Trump has prioritized efforts to calm the financial markets — trying to keep oil prices from exploding upward, stocks from cratering and interest rates from surging.

When the markets have flashed danger, Trump has been quick with a social media post or a remark to claim the war he launched last month could soon end. He’s publicly declared that the markets are doing better than he expected, even with the S&P 500 stock index declining over...