The principal weakness of leftist political doctrine is, IMHO, an over-adherence to some of its Marxist roots, specifically that social class is to be defined in economic terms. If this is accurate then the class relationships that are the underpinnings of the Marxist historical dynamic are invalidated by the changing economic status, or as Paglia states In the US, salaries of skilled manual labourers have long exceeded those of mid-level office staff.
This is the real victory of the proletariat, not a "dictatorship" as Marx proposed, but a rise in economic status with regard to the bourgeousie that essentially eliminates their former class rivalry, at least in economic terms. In cultural terms this is debatable, and may be in part responsible for the red/blue nation split we noted in the last election.
There is a third measure beyond the economic and cultural, the political, the separation of which from the economic is not allowed under Marxist theory, nor is the class mobility which gave rise to it. America's self-proclaimed "ruling class" maps to economic or cultural classes very imperfectly, in fact, is rapidly becoming an entity of itself: Such concentration of power in the State creates its own tyrannical master class. The left stubbornly refuses to recognize this fact, preferring to ignore this class in theory and attempt to suborn it in practice. This dichotomy describes where Lenin left Marx, but that was three-quarters of a century ago and the left is yet to really account for that, preferring instead to substitute murky jargon for theory and increasingly stale cliches for practice.
Marx had a phrase for this, too, "alienation." It wasn't supposed to happen to the left.
Let's just put this in plain English. Manual laborers are rewarded more in a Marxian society because their loyalty is more easily bought. The thick-headed are a natural target for class warfare, since many of the simple-minded resent their smarter neighbors. Call it Marx's Revenge Of The Boneheads.
Michael