A common refrain among union critics is that Americans no longer need unions—that unions were well and good for the exploited sweatshop workers of a century ago, but today’s empowered Americans need no such crutch. 

With workers’ incomes falling, and with the United States leading all industrial nations in the percentage of its workers in low-wage jobs, it’s increasingly clear that today’s we need unions for many of the same reasons that the workers of 1912 did: They’re exploited and underpaid. But if it’s only the nation’s most exploited workers who need to band together, why have America’s most talented employees formed unions of their own?

The paradox of unions is that they are at once armies and democracies—an oxymoronic construct that means they can seldom be as efficient as a top-down organization, or as expansively deliberative as, say, an idealized New England town meeting. There no ideal equipoise for a union—some, in which member participation has atrophied, can be essentially autocrat; some are more democratic (although democracy can impede growth if members insist on making the union devote resources to servicing their needs at the expense of organizing new members). The better unions try to balance their dual roles, and that looks like what the Chicago Teachers Union did Sunday night.

Read the commentariat, or just subject yourself to the deafening consensus of enlightened opinion, and you have to believe that the beleaguered parents of Chicago’s schoolchildren are fuming at their city’s teachers' union, on strike now for a full week, and backing Mayor Rahm Emanuel’s efforts to shape up the school district.

Imagine America without unions. This shouldn’t be hard. In much of America unions have already disappeared. In the rest of America they’re battling for their lives.

Unions have been declining for decades. In the early 1950s, one out of three American workers belonged to them, four out of ten in the private sector. Today, only 11.8 percent of American workers are union members; in the private sector, just 6.9 percent. The vanishing act varies by region—in the South, it’s almost total—but proceeds relentlessly everywhere. Since 1983, the number of states in which at least 10 percent of private-sector workers have union contracts has shrunk from 42 to 8.

Following the 2010 elections, a number of newly elected Republican governors and legislatures in the industrial Midwest, long a union stronghold, moved to reduce labor’s numbers to the trace-element levels that exist in the South. A cold political logic spurred their attacks: Labor was the chief source of funding and volunteers for their Democratic opponents, and working-class whites, who still constitute a sizable share of the electorate in their states, were far more likely to vote Democratic if they belonged to a union. The fiscal crisis of the states provided the pretext for Republicans to try to take out their foremost adversaries, public-employee unions.

Put aside for a moment the particulars of the Chicago teachers’ strike and look at the broader picture. Rahm Emanuel is only one of a number of Democratic mayors and governors who are going after public-employee unions. In Los Angeles, Mayor Antonio Villaraigosa is also at loggerheads with the city’s teacher union. In San Jose, a Democratic mayor and city council scaled back the city employees’ pensions (and so did city voters when they were asked to ratify that decision). In New York, Governor Andrew Cuomo has tangled with a number of public-sector unions. The battle between management and labor seems to have spread to the very center of the Democratic Party.

The third and final night of this week’s Democratic Convention may have lacked the fireworks we saw on the first two. Michelle Obama and Bill Clinton were eloquent in different ways, and weren’t matched by Barack Obama or Joe Biden on the convention’s closing night. That’s not to say that the closing night wasn’t effective, however. By focusing above all on two of Obama’s decisions – to save General Motors and Chrysler and to send in the Seals to take out Osama bin Laden – Obama and Biden emphasized the two most politically potent contrasts, especially on the latter point, they could draw with Mitt Romney and used those contrasts to make their most telling attacks on Romney yet.