On December 20th, the Dow Jones Industrial Average closed at 49,625.97, up 230.81 points or 0.47%, after the U.S. Supreme Court ruled that tariffs imposed by President Trump under the International Emergency Economic Powers Act (IEEPA) were illegal. Initially, the market opened lower, down 72.16 points at 49,323, due to concerns over an economic slowdown highlighted by disappointing GDP estimates released earlier by the Department of Commerce. However, the Supreme Court's decision shifted the momentum in the market, and buying quickly gained traction.

The ruling by the Supreme Court arrived approximately half an hour into the trading day, overturning previous legal justifications for the tariffs which had been a point of contention and economic uncertainty. Following the announcement, the Dow peaked at over 300 points above the previous close, signaling a strong investor response to the decision. Major stocks such as Amazon and Apple also saw significant gains, with Amazon up 2.56% and Apple up 1.54%, reflecting widespread confidence among investors in the wake of the ruling.

This development not only underscores the volatility of the stock market in response to legal decisions but also raises questions about the future of trade policies under the current administration. Analysts suggest that this ruling could lead to a reevaluation of similar tariffs and impacts on international trade relations, further affecting market dynamics if other tariffs introduced by the Trump administration are challenged or overturned. Such outcomes could have substantial implications for the broader economy and investment landscape in the United States.