In 1942, American leaders were faced with a decision: Should the United States engage in "from the sea" operations in two distant theaters or should operations be delayed in one theater while being undertaken in the other. While at the time the risk of the actions -- at worst the loss of the war in one or both theaters and at best, a prolonging of the war -- were substantial, ultimately, the rewards outweighed the risks.
It was not until the mid-April 1942 Doolittle raid over Tokyo that Americans had a sense that the United States was striking back at the Japanese. United States forces halted the Japanese advance in the Coral Sea in early May and by early June inflicted serious damage on the Japanese fleet at Midway. Despite these actions, American forces had yet to engage significant Japanese ground forces. By mid-August, American aircraft had begun participating in bombing raids on the European continent., while simultaneously an American ground force was being massed for the eventual invasion of the European continent. Although Americans had been lost in both theaters of operations, the American public had yet to feel invested in the war in the European theater.
The United States was committed to a "Europe First" strategy - a strategy where we would commit the bulk of our effort to defeating the Axis powers in Europe, while fighting a defensive/containment war in the Pacific. Our national "instinct" was to immediately fight on the European continent, while the British, our principal ally in Europe, preferred a policy of peripheral containment, working first to clear the Mediterranean before moving onto the continent. .
The American leadership, both President Roosevelt and the military, understood the need for American involvement in the European conflict, where our support was necessary for the very survival of Great Britain and Russia. They also understood that delaying American involvement in the European conflict ran a significant risk of losing the support of the American public; a public more focused on the war with Japan, the enemy who had directly inflicted pain and damage on the United States.