It's true, Biden might unintentionally say something that would plunge Europe into war...and Hillary is busy cleaning the Foreign Policy Czar's executive washroom that day.
But, mainly, for Obama to acknowledge the Wall or that the Cold War was the seminal conflict of the last half of the 20th Century, with global destruction in the balance, and that it was finally won by 12 years of hardheaded Republican rule, well Hell, that just ain't gonna happen.