There has never been a spring planting season like this one. Rivers topped their banks. Levees were breached. Fields filled with water and mud. And it kept raining. It was raining when U.S. farmers, a year into being squeezed out of the world’s largest soybean market by the trade war with China, were supposed to start putting down crops. It was raining when President Donald Trump risked starting a feud with Mexico, the biggest buyer of U.S. corn, by threatening to slap tariffs on its exports.