Perhaps The Treasure of the Sierra Madre was showing in Cambridge that weekend and each economist realized that he would always have to worry about the other two guys.
The economists the weekend that the Treasure of the Sierra Madre was showing in Cambridge began to stress about their competition. 
mnli hypothesis: The economists the weekend that the Treasure of the Sierra Madre was showing in Cambridge began to stress about their competition.  premise: Perhaps The Treasure of the Sierra Madre was showing in Cambridge that weekend and each economist realized that he would always have to worry about the other two guys.