I maintain that the right has actually drifted to the Left, but the Left has gone so far radically to the left that gulf between the two is much wider.
Plus, the Left has nuked and purged their moderates to the point there is a large no-man's land between the two parties. The last person on the Left I had any respect for, Zell Miller, is long gone. And seeing how liberal the Republican Party has largely become, that says a LOT about where the Left really is.
You are correct in the relative shifting of the two parties.