It started with the concentration camps.
In the first American offensive action of the war, US marines land on Guadalcanal.
The German 1942 offensive in the USSR began well, so well that Hitler split the offensive into two parts. The German Army was advancing on Stalingrad and threatening to cut Russia off from its oil fields in the Caucasus.
The US military went into the war just itching to invade France and take on the Germans ASAP. It was up to the British to talk them down, though the Allies did attempt a raid on the French coast at the port of Dieppe. Meanwhile, German intelligence infiltrated saboteurs into the United States.