The UK ceded Poland to the Russians because they had no choice. The same applied to the US. Neither was willing to risk a war with the Soviets over Poland, or for that matter any other Eastern bloc country. That's irrelevant to the discussion though because the UK, US, and France WERE willing to fight Germany over Poland. That's the entire point.
Caen had already fallen by July 20th. There was no longer any way for Germany to eject the Allies from France at that point. The US breakout along the coast started less than a week later. No change in leadership was going to prevent that from happening.Oh, and Overlord was far from decided in July of '44.
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