No American was going to die to save former Nazi allied nations from the (what I am sure most Americans considered the rightful) wrath of the Soviets.Well, and in addition, most Americans I would say, perceived the Soviets as present allies, not future adversaries. I believe Churchill cringed at what was coming but FDR posed as the supreme strategist who had "Uncle Joe" well in hand.
Churchill was a good tactician but a horrible strategist (Italy was not the soft underbelly of Europe and his Gallipoli was a disaster). Even if FDR listened to Churchill - what was the alternative? None existed beyond cutting of supplies to the Soviets - at the time we still thought we needed them in Asia to fight Japan and at the time of Yalta Germany was far from defeated. If we cut off the Soviets Stalin would have cut a deal and Hitler would have still held on to a huge chunk of Eastern Europe.
History is no as black or white as we may like it to be. Time also distorts reality. Bush was speaking of an understanding of history from a modern standpoint - not how events played themselves out at Yalta.