Picture the Titanic, except filled with lettuce instead of passengers. Now picture five Titanics filled with lettuce, plus another half-filled ship. Picture this armada of ships, laden with romaine, spring mix, red leaf, green leaf and iceberg, all setting sail for Canada. This is how much lettuce our country imports every year: 265,000 metric tons in 2022 alone. Almost all of it comes from the U.S., and the majority from one state: California. For years, this fleet of imported lettuce arrived without incident, supplying a steady stream of leafy greens to our frostbitten country. But in the past six months,...