A Question on the Source of a Cultural Reference

In commenting on the impact of yesterday's primary election results in the United States, GOP strategist and CNN contributor Alex Castellanos noted the following:

Tomorrow, [John McCain] can get started. He'll have the [Republican National Committee] behind him. He'll have a broad base of financial support. It's a big step. Meanwhile, it looks like the Democrats are engaged in the land war across Russia, so he's got a big advantage now.

My question is this: in using the metaphor of a "land war across Russia", what is the direct background of Castellanos' cultural reference? I would argue that the final background is, indeed, the historical notion that a land war in Russia is about the hardest and most grueling thing a European army can attempt. However, is this also the direct background behind Castellanos' remark? Or is the direct cultural reference, which itself then refers to the historical background, Vizzini's remark in The Princess Bride that the most famous of the classic blunders "is never get involved in a land war in Asia"?