President Trump on Wednesday made the case to a skeptical American public that the military operation in Iran is necessary to stop Tehran from building a nuclear weapon.

President Trump delivered a primetime address about the war on Iran on Wednesday evening, more than a month after hostilities commenced. Trump’s decision to launch the war, in conjunction with Israel, has come to look more and more risky. The conflict has been unpopular since its inception. Soaring gas prices and turbulence on the financial...