Only Hillary Clinton will know exactly why she said that Donald Trump "is becoming [Islamic State's] best recruiter."
By the typical political calculus, it qualified as a good zinger – something likely to be replayed again and again the next day. It also marked a shot across Trump's bow in advance of a potential general election faceoff next November.
Yet beneath the theatrics of the comment lies one of the most significant points of debate in the war against the Islamic State: What role should Americans themselves play?
Some Republicans, such as Mr. Trump and Sen. Ted Cruz of Texas, have cast the conflict in the terms of a conventional war – whether talking of temporarily banning Muslim visitors or of "carpet bombing" Islamic State strongholds in Syria and Iraq. In this scenario, the defeat of the Islamic State occurs by military action abroad and vigilance at home, and residents are asked to stay resolute.
But Democrats such as Clinton and particularly President Obama have been more likely to see the conflict in social terms, arguing that incautious policy and rhetoric will only strengthen Islamic State. In this scenario, overseas military might and domestic surveillance are crucial, but so is the active participation of Western citizens themselves – to stem the sense of Muslim alienation in their own communities that fuels Islamic State recruitment.
In taking on Trump Saturday for his proposed Muslim ban, Clinton was fundamentally asserting that how Americans act and what they say on the homefront has the power to strengthen or weaken the Islamic State. In that way, her comments laid out a stark choice – between one vision that seeks only to shield Americans from the Islamic State and another that calls upon them to be active agents in the solution.
So far, numerous media fact-checking groups have found no evidence that the Islamic State is actually using Trump's statements as part of its recruitment drives. But the deeper point is relevant, many who follow the Islamic State closely say.
Nicolas Hénin was held hostage by the Islamic State for 10 months. The Westerners beheaded were his cell mates. Infamous executioner Jihadi John nicknamed him "baldy." After the Paris attacks, however, the Frenchman was moved to sadness but not to hate or revenge, he wrote in an article for The Guardian. That, he said, would simply have played into the Islamic State's hands.
They will be heartened by every sign of overreaction, of division, of fear, of racism, of xenophobia; they will be drawn to any examples of ugliness on social media.
Central to their world view is the belief that communities cannot live together with Muslims, and every day their antennae will be tuned towards finding supporting evidence. The pictures from Germany of people welcoming migrants will have been particularly troubling to them. Cohesion, tolerance – it is not what they want to see.
Mr. Hénin's response is not an act of idealism, experts say, but an integral part of a successful counterterrorism strategy.
"Counterterrorism tries to do two things: You try to neutralize existing terrorists and you try to not breed new ones," said Max Abrahms, a political scientist at Northeastern University who studies terrorism, to The Daily Beast.
The Islamic State exists only because it can skulk on the margins – controlling only the remotest reaches between two failing states. Its most potent weapon is its ideology – the claim that the West is fighting an apocalyptic war against Islam and that all true Muslims must rally to its cause. And its only tactic beyond its bare patch of land in the Middle East is to use its ideology to exploit and exacerbate rifts in society though the Internet.
The relative weakness of the Islamic State shows that few Muslims believe this ideology. But making society's rifts worse only helps the Islamic State, Professor Abrahms argues.
"The surest way to breed new ones is if you’re indiscriminate – for instance, punishing non-violent, moderate Muslims."
For his part, Trump has said his proposed temporary ban on Muslims entering the United States is "common sense," telling MSNBC's Joe Scarborough: "When you say you’re afraid, I think you should be afraid. You should be afraid of the other side, not my side."
To supporters, his proposals make sense for a nation in some ways on war footing. "Muslims are clearly more susceptible to the siren call of terrorism and more likely to be radicalized on the Internet and in mosques than are Christians at church or Jews at synagogue," writes former presidential candidate Pat Buchanan.
Trump likened his proposed ban to what President Roosevelt did in World War II.
While many historians point to such actions as a low point of Roosevelt's presidency, Clinton appeared to be making a different point Saturday night: This war is different.
To Dominic Tierney of The Atlantic, extremism becomes its own cause and effect – a cycle that survives by feeding upon itself in a "global confederation of extremists." One extremist action provokes a reaction.
In casting Trump as an inadvertent Islamic State recruiter, Clinton has responded to his supposedly extremist rhetoric with a flourish of her own.
But the underlying question she raises draws a bright line between two sharply different worldviews of how to defeat the Islamic State.