The collapse of the private sector union movement

That topic is explained briefly by Mickey Kaus over at his blog. (Hat tip to Instapundit.) As Kaus explains, the percentage of private sector workers who are members of a union is flat in comparison to last year -- and both years are pretty dismal in regard to overall numbers. From a high of 35% at the mid-point of the century, private sector workers are now unionized at a rate under 7%. That's an astounding collapse. What's the cause? Kaus doesn't offer any, although I would speculate that the decline of American manufacturing combined with the increased leftism of the union movement as a whole is what is doing the unions in.