[231]
When World War II began in September 1939 with Germany's invasion of Poland and Britain and France's subsequent declaration of war upon Germany, Roosevelt sought ways to assist Britain and France militarily.[232] Isolationist leaders like Charles Lindbergh and Senator William Borah successfully mobilized opposition to Roosevelt's proposed repeal of the Neutrality Act, but Roosevelt won Congressional approval of the sale of arms on a cash-and-carry basis.[233] He also began a regular secret correspondence with Britain's First Lord of the Admiralty, Winston Churchill, in September 1939—the first of 1,700 letters and telegrams between them.[234] Roosevelt forged a close personal relationship with Churchill, who became Prime Minister of the United Kingdom in May 1940.[235]
The Fall of France in June 1940 shocked the American public, and isolationist sentiment declined.[236] In July 1940, Roosevelt appointed two interventionist Republican leaders, Henry L. Stimson and Frank Knox, as Secretaries of War and the Navy, respectively. Both parties gave support to his plans for a rapid build-up of the American military, but the isolationists warned that Roosevelt would get the nation into an unnecessary war with Germany.