Trump on Monday said the United States would ship "billions of dollars' worth" of military equipment to NATO members, paid for by the alliance, to be handed over to Ukrainian forces battling grinding Russian advances. Trump had earlier this month suggested NATO would "100 percent" pay for U.S. weapons, which would be sent to Ukraine.

President Donald Trump has finally found a way to like arming Ukraine: ask European allies to donate their weapons, and sell them American replacements.

But using heavy tariffs to stop countries buying Russian oil would be a blunt tool – and while they could significantly squeeze Russia’s war funding, they could also unleash more havoc on the rest of...