Assume that the Pearl Harbor surprise attack proceeds as OTL, but that once General Douglas MacArthur receives word of the bombings, he orders his air command on Clark and Iba air-fields to bomb the Japanese invasion fleet at Formosa while the Japanese are still hemmed in by early morning fog.
Let's also suppose that instead of seeking to repel the Japanese invaders at the beaches, MacArthur instead follows War Plan Orange, and in the intervening years before December 1941 he fortifies the approaches to the Bataan peninsula and sets up the equivalent of the Fort Stotsenberg supply base at Mariveles.
This helps to ensure that though the Japanese would eventually force their way through Luzon, his troops on Bataan would be well-supplied (or at least in better circumstances than occurred in OTL) and ready to meet them in pre-prepared positions with a massive supply base in their rear. Obviously this would result in a much longer siege through 1942 with significantly higher casualties for the Japanese who would presumably have to pull troops from other pending operations throughout the Southwest Pacific to subdue the well-supplied (and better-fed) American-Filipino garrison on Bataan and Corregidor.
And don't forget that there are other commands on the other islands throughout the Philippines archipelago that the Japanese would also have to conquer.
And before I forget, also imagine that Gen. Douglas MacArthur would still be pulled out of Corregidor and spirited to Australia per presidential orders in February 1942 as in OTL, but that Chief of Staff George C. Marshall would not alter MacArthur's command structure by promoting Gen. Jonathan Wainwright as commander of all American and Filipino units in the Philippines (as opposed to just Corregidor and Bataan, as MacArthur had intended with himself remaining as supreme commander in the Philippines).
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How differently would the war in the Pacific have turned out had the Japanese faced longer and stiffer organized resistance in the Philippines, along with a command structure that still left Gen. Douglas MacArthur as supreme commander in the Philippines?