Oil producing countries are bracing for a bumpy ride this year, with a precipitous drop in prices to the lowest levels in four years seen as the initial, alarming sign of looming turmoil. A price drop benefits any country seeking to cut its fuel bill. But in oil producing nations, lower prices can feed economic troubles, and sometimes political unrest, as governments slash spending. Analysts who had already been predicting lower oil prices because of softening demand amid increased global production said the possibility of a tariff trade war and the overall climate of uncertainty could well deepen producers’ woes....