Question for our history buffs: at what point did victory become unachievable for the Axis?
My view: after the failure to take Moscow in 1941. I do think it was likely that the government would have fallen. This wasn't 1813. If the beating Soviet forces took all along the front had been capped off by the fall of the capital I think that would have been the end for the Soviet government or at least Stalin. Negotiations would have ensued. The survival of the Soviet state coupled with the entry of the USA made victory impossible, IMO. Not a stalemate of some kind. I think that was still achievable through the Summer of 1943.
I am not considering any other what-ifs here (e.g. no declaration of war on the US by Germany, increased cooperation between the Japanese and Germans etc.)