The Internet is facilitating a generational transition within America's advocacy group system. New "netroots" political associations have arisen in the past decade and play an increasingly prominent role in citizen political mobilization. At the same time, the organizations that mediate citizen political engagement and sustained collective action are changing. They rely upon modified staff structures and work routines. They employ novel strategies and tactical repertoires. Rather than "organizing without organizations," the new media environment has given rise to "organizing through different...