There are three things that could happen that would give Japan the resoures it would need to either deter or take on the United States.
One, a cynical moderation of it's racial policies to recruit anti-colonist forces in India and Asia. Japan was never able to fully exploit the divide between the Allies and their colonies because of harshness of their occupation policies.
Two, the fall of Britain, causing a power vacuum in the Far East. If Lord Halifax had become Prime Minister instead of Churchill there was the possibility of a political collapse in England, which would lead to surrender. Those Anti-Nazi forces would move to Canada, and President Roosevelt would have to become far more involved in Europe even as the risk of losing the 1940 election. Even if he had lost, his Republican opponent, Wendall Wilkie, was also Anti-Nazi and efforts of the Third Reich would continue.
And Three, Japan does not become a member of the Axis. While the U.S. and Free British and Commonwealth forces would be battling in Europe, Japan could exploit the situation independently. French Indo-China and the Neatherland East Indies could be conquered outright, and India and Malaysia could be subverted, potentially giving Japan resources and manpower to exploit.