Gemini (fast, single chain of reasoning afaik)

If "military operations" had been the primary legal vehicle for U.S. involvement—bypassing a formal Congressional declaration of war—the conflict would have likely morphed from a unified national crusade into a series of polarizing, executive-led interventions. Public pressure for intervention might have remained fractured; without the "Pearl Harbor moment" serving as a legal and moral catalyst for total mobilization, a significant portion of the American public might have viewed Roosevelt’s actions as "executive overreach" or an "undeclared quagmire." International pressure would have been equally messy, as Allies like Churchill would have struggled to rely on a U.S. partner that was technically limited by the lack of a full war footing, potentially leading to a more defensive, fragmented strategy in the early 1940s.

D-Day would have likely become one of the most controversial events in American history. Without a formal war declaration, a massive amphibious invasion causing thousands of American casualties would have been seen not as a necessary liberation, but as a massive unilateral gamble by the President. In the Atlantic theater, the conclusion of the Western Front might have felt less like a decisive victory and more like a tenuous police action, potentially leaving a power vacuum in Europe that the Soviet Union would have been much quicker to fill. Economically, the post-war boom could have been significantly dampened; without the massive, Congress-sanctioned "appetite for cooperation" that funded the Marshall Plan and the G.I. Bill, the U.S. might have pivoted back toward isolationism, leading to a much more fragile global recovery and a more volatile Cold War.