I know they did attack Alaska, but I meant a location that would swing public interest more than a couple small islands.
For the Australian part I’m not seeing a reason to think they’d end up winning as a result of the potential invasion. If they launch a full attack on Australia they overstretch their forces even more than they already were. How would they have the forces to do so and to maintain control of the areas? Plus that could cause the UK to take on a more active role in fighting Japan, while they didn’t have as much of an incentive to before. I do agree that overall without American presence Japan would probably have the opportunity to have extra oil sooner than they did, but I really don’t see how that leads to a Japanese victory, it seems more just changing the timeline of when things happen.
For the part about assuming Hitler convinces Italy to suck less I just feel like you can always say that. Fact is, Italy made some stupid decisions, and I don’t think the stupid decisions were influenced by the US in particular. Nor do I see a reasonable decision that Italy would have made that would have changed the outcome of Operation Barbarossa, especially with the clashing sentiments that would have been brought up with their inherent differences in how they viewed Jews and some other groups of people. Nazi Germany just fucked up. Additionally, the Italian choice to go after Egypt would be unaffected here because they invaded Egypt prior to the attack on Pearl Harbor anyways. So in this case, there’s nothing majorly different between our timeline and this alternate one, and no reason to view that as an expected difference that would occur.
As for Europe there’s no way Europe falls, with or without the help of the US militarily. The main US offensive was Operation Overlord. Had that not happened, the post war map would look different, sure, and the Soviet Union would have an even higher casualty count. Operation overlord helped speed it up, and changed things at the negotiating tables. But it’s widely accepted that the Soviets would have defeated Germany regardless. It was a game changer to the post war world since having military offensives gives a country a lot more power to negotiate, but the Soviets had been on a offensive path for over a year, while Germany had been on the defensive, and had almost no land in their control in the USSR. As for China, if Japan was defeated in this timeline (which seems more likely than not) then there we go. The only way China falls is if Japan completely defeats the Allies despite their victory over Germany, which just seems overall unlikely.
As for Churchill well yeah. Churchill was a good wartime leader, but he would be a horrible peacetime leader. The people knew that, so the voted him out before he does something absurd and gets them into another war or whatever. Different eras and situations require different traits in leaders.
Oh jeez this is long

TLDR I can’t see a situation where American forces change whether or not the Allies or Axis win, only details such as post war world allocation and how long it takes and whatnot. But this isn’t even considering the scenario where a different US target is bombed to bring the US into the war, which I consider the far more likely one here anyways.