Final answer:
The position of isolationists in 1940 was weakened by the global threats posed by totalitarian regimes, the passage of Neutrality Acts that still led to a gradual shift towards aiding European democracies, and the reconsideration of isolationist policies by the Roosevelt administration amidst growing calls to support victims of aggression.
Step-by-step explanation:
The position of isolationists in 1940 was weakened by a number of factors. Firstly, the aggressive actions of totalitarian governments overseas, particularly those of Nazi Germany, increased the perceived threat to global peace and security, making an isolationist stance more difficult to maintain. In response to these growing threats, Congress passed a series of Neutrality Acts aimed to keep the United States out of foreign conflicts, but as tensions increased, the need for more proactive engagement became apparent.
President Roosevelt's administration demonstrated foresight in seeking to aid the European democracies under threat from fascist powers during his third term in office, and the desire of Americans to support victims of aggression grew. Despite initial resistance, the United States began reconsidering its isolationist policies, which is evident from Roosevelt's private communications indicating a willingness to support Britain and France against Germany.
Additionally, fears that military aid sent to Britain might fall into German hands if Britain was defeated, like France and Poland had been, underscored the urgency in building up the U.S. armed forces before becoming directly involved in the conflict.