Franklin D. Roosevelt (FDR): Pearl Harbor
In 1938, FDR wasn't yet sure what to make of Hitler. At home, Roosevelt faced strong pressure not to get involved in Europe from isolationists in Congress. While Roosevelt saw the potential for danger, he didn't yet know whether or not Hitler simply wanted a bit more land, or whether he actually wanted a war with the whole world.38
Just as he had remained vague on his "New Deal" plans while running for president in 1932, FDR prepared the nation for war by playing both sides of the coin. In early 1939, he espoused isolationism in his State of the Union address, but also asked Congress to spend $525 million on armaments, arguing that the best protection against war was a strong defense.39 When war did break out in Europe in September 1939, FDR worked to find a middle path between the demands of the Allies and the isolationists at home by proposing the Lend-Lease Act, in which the United States gave the Allies $50 billion of military aid.
Even without Congressional authorization, FDR began to engage Germany directly in the arena in which he had the most military experience—at sea. For most of 1941 the US and Germany fought an undeclared naval war in the Atlantic, as U-boats tried to sink convoys of supply ships protected by US naval forces.
Shortly before the 1940 presidential election, FDR told voters, "I have said this before, but I shall say it again and again: Your boys are not going to be sent into any foreign wars."40 Ultimately, of course, that is exactly what he did. Less than a year after winning reelection in the 1940 campaign, Japan launched a surprise attack on Pearl Harbor, plunging the US into the war. Congress declared war on the Axis Powers, and FDR officially became a wartime president.