What would have happened had Berlin been abandoned during the crisis? Many military experts believed it was a complete impossibility that Berlin could have been saved by an airlift rescue!
It turns public opinion in the Allied occupied zones strongly against them. The Soviets would see it as a sign of weakness and would carry out some other provocative act soon after.
Truman doesn't strike me as the one to do this.
Absolutely, perhaps if someone like Wallace was POTUS?
In spite of Popular Opinion, Wallace wasn't a complete idiot, by the time you get to the Berlin Crisis he's have learned his lesson after 1945-46 foolishness. Of course President Wallace opens the option to avoid the Berlin crisis completely, if German policy differs.