The social and political impact in the United States of the outcome of the investigation into the bomb attacks on the Boston Marathon is almost impossible to overestimate. It will, in all likelihood, define several key cultural markers for the next generation of Americans.

Although the country has been awash with violence of many different kinds, including various terrorist acts, this is by far the most culturally and politically significant since the 9/11 atrocities. Like 9/11, and the Oklahoma City bombing before it, the attack on the Boston Marathon has profound and national symbolic resonance. Nothing since September 11, 2001 compares in this regard.

Few facts are known and authorities say no suspects are identified or in custody. Therefore, a huge range of potential perpetrators with widely divergent motivations remains potentially culpable.

But within the wide range of possible scenarios, three obviously stand out. The culprits could be right-wing, anti-government American extremists. They might be some other kind of domestic extremists, or even a lone madman. But there is also the distinct possibility that the bombings may prove to be linked to some group of Muslim extremists, either foreign or domestic.

It is this last category that would have most impact.

Deep reservoirs of antipathy between the Christian West and the Islamic world, and ingrained stereotypes of Arabs and Muslims as hostile, violent and fanatical, informed a period of unprecedented Islamophobia in the United States following the 9/11 attacks. For much of the past decade it became possible to vilify and stigmatize Muslims or Arabs in general with little, if any, social and political cost. This was particularly true on the cultural and political right.

The manifestations of such bigotry have been deeply excavated elsewhere and need not be recited here. What is crucial is that in the past few years, the period of relative impunity for post-9/11 Islamophobia and anti-Arab racism was clearly starting to have run its course.

Crackpots were readily identified and increasingly shunned. Muslim Americans made significant progress in mainstreaming themselves and their image with their compatriots. And a significant pushback against bigotry emerged, including within the conservative movement itself.

If the Boston Marathon terrorist attacks are eventually linked to any kind of Muslim extremists, or even a deranged individual of Muslim origin, the likely impact is that this will set the clock back many years, if not a full decade, on the abating of the post-9/11 Islamophobia epidemic.

Muslims in general, however unfairly, will be identified more strongly than ever in the minds of bigoted Americans, particularly on the right, with political terrorism as a phenomenon. And many Americans who have been moving away from such prejudices will be drawn back into them. Officials will be once again tempted to rely on stereotyping as a tool of counterterrorism and law enforcement.

The calls for discriminatory measures—certainly against citizens of a list of Muslim countries, plus Cuba and North Korea (always thrown in for good measure), and possibly even against Muslim or Arab American citizens themselves—may again become shrill and voluble. And, once again, it could take a considerable effort to push back against them.

That such a reaction would be irrational counterintuitively makes it all the more plausible. Trauma, whether personal or national, typically does not produce, in the immediate aftermath at least, a fully rational response.

If, on the other hand, the culprits prove to be right-wing domestic extremists or any other persons without links to the Arab or Muslim worlds, or American communities, the crime could well prove a turning point in the opposite direction.

True, there have been dozens of violent incidents over the past decade in the United States that, as many have noted, had they been perpetrated by people of Arab or Muslim origins would have been far more notorious and used to promote fear and hatred. But none had the resonance or nationally traumatic quality of the Boston Marathon attack. And major terrorist attacks in Britain and Spain by Muslim extremists, or in Norway by a right-wing fanatic, had very limited impact on the American worldview.

In this case, however, if the criminals prove to be of Arab or Muslim origin in any way, this will strongly reinforce the association of that identity group with terrorism. But if it is not, it will surely help further break that already strained cultural association.

Whichever way it goes, the outcome is likely to have a massive, if not determinative, impact on the way terrorism and political violence are culturally associated and defined by an entire generation of Americans.

Does this mean that we’ve preposterously ceded the ability to shape our perceptions to small groups of crazy people? Sure it does. But that’s how human beings typically operate. And the rational corrective is invariably slow and painstaking.