As the U.S. economy sank ever deeper into recession, and as millions of Americans faced job loss, plummeting home values, and deferred retirement dreams, angry protesters rallied across the nation. Activists on the conservative side were first to arrive on the scene. Throughout the winter and spring, the Tea Party managed to shift blame for the recession to the Obama administration and demanded that it reduce spending. The burgeoning Occupy Wall Street movement could be the spark that progressive activists have been waiting for -- an opportunity to reframe the economic crisis and generate broader support for government economic stimulation and for measures to promote greater equality. Occupy Wall Street's success will depend, in large part, on whether protesters effectively manage violence (as the Tea Party has) or fail to do so (as in the 1999 protests against the World Trade Organization in Seattle).

Protest movements must always walk a fine line between nonviolent and violent action. The power of protest comes from its capacity to disrupt business as usual. Without such disruption, it fails to give opponents any incentive to grant concessions or to give the media any reason to pay attention. Yet violence can generate a significant backlash among the general public, which in turn provides authorities with the cover they need to crack down.

Negotiating between impotence and overaggression is difficult. It is often police action that triggers violence at large protest events; research has shown that police crackdowns can quickly transform nonviolent events into violent ones. This was certainly the case in many campus demonstrations of the 1960s and 1970s. Excessive force used by police can work to the protesters' advantage, winning them public attention. For their part, the Occupy Wall Street protesters already seem to have benefited from media coverage of the police using pepper spray to disperse them and of a chaotic mass arrest on the Brooklyn Bridge.

Still, relying on police overreaction to spark public interest is not an effective strategy for building momentum. It may win some sympathy, but the average American actually has a fair amount of tolerance for aggressive policing. For example, in the wake of the shooting of Kent State students by members of the National Guards in 1970, a Gallup Poll showed that a majority of Americans blamed the students, not the guards, for the shooting. Meanwhile, police forces, particularly in major cities, are well aware that excessive force can energize protest campaigns. Thanks to the hierarchical structure of police organizations, it is easier for a police unit to exercise restraint than it is for protesters, who have no formal structure.

This is not to say that the Occupy Wall Street movement is a lawless "mob," as Representative Eric Cantor, the House majority leader, recently characterized it. People who participate in such protests are typically deeply connected to their community. It is their connectedness that makes them aware of opportunities to protest in the first place. The crowds gathered in the streets of New York and in other cities across the nation, then, are not made up of isolated strangers; they are composed of many small, well-organized groups.

This structure will go some way toward policing behavior, but it cannot control violence completely. Each grouping of participants has different goals, ideals, and motives for acting. And, because progressive activists place high value on democratic participation and freedom of expression, they are often reluctant to rein in participants who are acting counterproductively. There are always fringe groups who want to take advantage of the protests to make their own statement -- sometimes employing violence as a means of capturing attention for themselves. In such cases, the violence can potentially spread through the crowd. Protest participants who planned on peace may be willing to join in the fray once the first rock or bottle has been thrown. Then, an aggressive police response will draw in even more protesters. That is exactly what happened in Seattle.

Such an escalation of violence is most likely to occur when a high proportion of participants have become skeptical about their chances of producing a desirable outcome through peaceful protest. Occupy Wall Street has not yet reached that point. As unhappy as many progressives are with the cautious approach thus far taken by the Obama administration, they have not abandoned hope. Public opinion is still in play. Obama's approval ratings are low, but the approval ratings of Republicans in Congress are lower. If the Occupy Wall Street protest can sustain itself peacefully, it could redirect anger over the economy toward corporations. This would, in turn, provide the Obama administration with more room to promote its progressive agenda.

Protests are most effective when their means reflect their message: in this case, that it is time for the rational majority of the country to stop letting special interests run wild. To be sure, conservative opponents, as well as some members of the media, have criticized the Wall Street protesters for failing to set out that demand clearly and coherently. Yet it is no accident that the protesters first decided to march on Wall Street. Historically, opposition to Wall Street has been an effective rallying point for those who are angry about economic circumstances -- this holds true for reactionary populist organizations such as the Ku Klux Klan as well as for progressive organizations. (Like Occupy Wall Street, many populist organizations believe that big business has co-opted the United States' democracy. For groups such as the Klan, meanwhile, Wall Street greed typically is connected to claims of vast Jewish conspiracies that aim to channel economic concerns and insecurity into support for an extremist agenda.) As millions of Americans deal with economic hardship and insecurity, nameless and faceless "fat cats" are ideal villains. And, as long as the protesters keep public attention focused on Wall Street's dastardly deeds and not on violent and unruly behavior in their own ranks, they will surely meet with some success.