Years of droughts in Mexico have already fractured its sugar exports to the US. Now President Donald Trump’s proposed tariffs risk making the once-lucrative trade relationship even worse for America’s top foreign supplier of the commodity.

Trade agreements between the two nations were meant to create a reliable flow of affordable sugar to the US. But the system has unraveled, with more imports now coming from everywhere else. Shipments from Mexico are expected to fall to a 17-year low in 2025, leaving the Latin American nation with a smaller sliver of the market than it expected …

With five trucks and a tractor to his left and a sea of leafy green before him, Dean Haubenstricker lines up his harvester and starts it forward. The high-tech machine digs up brown sugar beets, lops off their tops, and conveys them to an onboard storage bin.

Mr. Haubenstricker’s son Josh arrives alongside with the tractor and a trailer, allowing his father to discharge his beets even as he continues to harvest, and then shuttles them to a waiting truck, which whisks them off to storage. It’s as elegant and efficient a harvest as one will see in American industrial agriculture. …

Bonbons and candy canes may dominate the American holiday aesthetic, but US confectionery companies are feeling anything but jolly as they head into one of the sugar market’s tightest years in recent memory.

Prolonged droughts in major cane-producers Mexico and Louisiana have helped push US sugar futures to the highest ever for this time of year and forced users to turn to high-cost imports instead. Sweets-makers paying up to snag supplies are choosing to protect their margins by raising prices for consumers — and hoping shoppers don’t balk at the mark-up. …