Hours after a truck plowed along a Manhattan bike path on Tuesday, Americans returned to a debate that has become a vessel for some of the most contentious questions dividing an increasingly polarized society: When is an attack terrorism?
A month ago, when a gunman opened fire on a crowd of concertgoers in Las Vegas, killing dozens and wounding hundreds, the attack was not broadly branded an act of terrorism. But that label was immediately attached to the attack on Tuesday that killed eight people, setting off another round of a fierce national debate.
On the surface, this could be considered a straightforward question of motive. Terrorism is defined as an attack on civilians meant to frighten a larger community for political purposes.
But the new generation of Islamist terrorism, conducted by individuals citing far-off inspiration, has blurred the distinctions between terrorist and disturbed loner. So have recent mass shooters who show signs of both mental illness and an attachment to vague ideological causes.
As a result, terrorism is often in the eye of the beholder, determined as much by the attacker as by the community that is targeted, which must decide whether the attack represents a broader threat requiring a response.
Each attack, then, quickly sets off a zero-sum debate over the related issues of gun control, immigration or religious tolerance — some of the most divisive issues in the country — litigated in a moment of national duress.
The Las Vegas attack, for some Americans, typically those on the left, represented the terrorism of unchecked gun laws.
Classifying the Las Vegas attack as terrorism might mean classifying guns as national threats requiring a response. The right would see this as an attempt to tar all gun owners and conservatives.
Attacks like the one in New York, led by a man from Uzbekistan who shouted "Allahu akbar," are seen by many on the right as stemming from the wider threat of uncontrolled Muslim immigration. If it is an act of terrorism, as Mayor Bill de Blasio and others have defined it, then the attacker cannot be dismissed as a disturbed loner.
More than 16 years after the Sept. 11 attacks, many Americans, particularly on the left, are questioning the readiness with which lone Muslims are defined as terrorists while lone non-Muslims are deemed "mass shooters."
Even if the label fits in individual cases, they say, the inconsistency suggests a tendency to see Muslims as part of a hostile fifth column and white male killers as exceptions.
Defining terrorism, then, has become another way of debating who belongs and whose concerns matter — and at a moment of perceived danger, when listening is hardest and shouting can feel necessary. It has become a perfect vessel for Americans' growing tendency to see their political opponents as not merely fellow citizens with whom they disagree, but as threats to their safety and security.
That is a recipe for increased polarization and hostility at a moment when Americans are already dangerously divided.