The tripartite pact comitted Italy and germany to declare war on the US once Japan had.
Japan had already broken the alliance pledge when it refused to declare war to Russia after Barbarossa. What goes around, comes around. Hitler and Mussolini delcared war out of megalomanic undervaluation of the American war potential and overvalution of the benefits that unrestricted submarine warfare could bring against Britain. A wiser strategic counsel should have led them to the realization that America ought to be kept out of the war in Europe at all costs.
Do you realise just how much further those middle-east fuel supplies are from cairo??
Nowhere further enough that the Italo-Germans can't reach them, if the Germans throw the bulk of their potential here, and the Italians get some decent doctrine and equipment, before or after Barbarossa. The Axis would have a very good logistics hub in Alexanderia, and can grab others in Palestine and Lebanon/Syria as they advance. And if Vichy can be convinced to cooperate and open up the Syrian ports and airfields before the philo-Axis Iraqi government is overthrown by the British, the distance to cover is short before Syria and Iraq can be secured, the British in Palestine trapped into a strategic vice, and the philo-Axis governments in Iraq and Iran buttressed against British offensives.
Why does US L-L miraculously stop to Russia, it started well before the USA was at war?
The Congress and the American people were no lovers of Bolshevik Russia and Land-Lease was controversial enough as it was, and enlarging it to Russia even more controversial. If the Axis assumes a defensive stance against Britain in Europe and the Atlantic, only going on the offensive in Africa, no BoB and no u-boats, and makes public offers of a white peace, Britain shall not register as deadly threatened to many Americans, and giving Land-Lease to it shall be even more politically controversial, in the face of widespread isolationaist opinion. In these conditions, it may be safely assumed that some Land-Lease to Britain would still be approved, but the much more controversial one to Russia would not. Roosevelt had only so much political capital to spend on his internationalist policies.