The Islamic State group's claim to have inspired this week's San Bernardino massacre raises the question of what kind of threat it poses after a year which has seen record numbers of alleged jihadists arrested in the United States.
Much is unclear approximately the motivation of the young Muslim couple who allegedly attacked the husband's co-workers at a workplace holiday party in San Bernardino, California on Wednesday, killing 14.
But the FBI is investigating the attack as an act of terrorism after finding evidence that the pair were inspired by extremist ideology & may have made an online pledge of allegiance to the Islamic State group.
This came as a surprise to many as the nondescript target was not a symbolic site & the couple — recent parents Syed Farook, 28, & Tashfeen Malik, 29 — are not thought to have been on any watch list.
But perhaps the attack, which otherwise bore the usual hallmarks of the mass shootings that have become so usual in the United States, should not have surprised?
Alexander Meleagrou-Hitchens, head of research at the international Centre for the Study of Radicalization & Political Violence, told AFP trouble has been long brewing.
"Since at least 2010 jihadist strategists & ideologues have called on & inspired Muslims in the West to do one of two things: Either join a jihadist group fighting abroad or, if they are going to stay in the countries which are waging a supposed war on Islam, they should carry out attacks using any means at their disposal," he said.
– High-powered firearms –
Despite its leading role in overseas military actions against Islamist networks like Al-Qaeda & the Islamic State group, the United States does not face a domestic jihadist threat on the scale of its European allies.
"However, in Europe so-called 'lone wolf' attackers cannot easily obtain their hands on high-powered firearms," Meleagrou-Hitchens told AFP.
"The problem for the United States is that these type of jihadists can arm themselves, legally, & then become almost as deadly as highly trained jihadists with formal connections to groups abroad.
"For me, it has always been a matter of time before a group of homegrown jihadists in America received their hands on firearms & carried out an attack like this, it is such an obvious & effortless thing to do."
This year has seen record numbers of arrests of suspected extremists, many of them victims of FBI sting operations yet others with ties to foreign groups deemed "terrorist organizations" under US law.
According to a major study of US jihadists released this week by George Washington University, 250 Americans have traveled or attempted to travel to Syria or Iraq to fight for the IS group's so-called "caliphate."
There are 900 active investigations against alleged IS sympathizers spread across all 50 US states & 71 have been charged with "IS-related" activities since March. Fifty-six of these suspects were arrested this year.
In the case of Wednesday's attack, however, the FBI has found no evidence that the couple was acting directly on behalf of an IS leader.
It was not until Saturday that IS called the perpetrators "soldiers" of its caliphate in an English-language radio broadcast & "supporters" in Arabic.
Experts following the threat said the core group seemed as surprised as anyone by the attacks.
Rita Katz, director of private terror watchdog the SITE Intelligence Group, told AFP that during last month's IS attacks in Paris the group had flooded the Internet with celebratory propaganda, some of it apparently pre-prepared.
But this week, the usual jihadist online forums were silent until news emerged from the US investigation that the couple were Muslims who had met in Saudi Arabia & had apparently found their own way to radicalization.
– 'Flooding Twitter' –
"They didn't celebrate it. It was nothing compared to what we usually see. It took them two days to come out with anything," Katz told AFP. "Now if you go on Twitter, it's a totally different story. They're flooding Twitter now."
Katz said police photographs of pipe bombs the couple had prepared resembled the detailed diagrams provided for so-called "lone wolf" attackers in Al-Qaeda's online English language magazine "Inspire."
And the suspects' decision to mount their own raid rather than joining an organized cell reflected instructions posted in the Islamic State's publication "Dabiq" — named after the Syrian village where the group expects to make its last stand against infidel forces at the world's end.
The second edition of Dabiq published in July last year told supporters who were unable to make a pilgrimage to fight for the caliphate; to pledge allegiance, or "bayat" in Arabic, to the IS leader; & to launch domestic attacks.
"Try to record these bayat & then distribute them through all forms of media including the Internet," it said.
This, FBI agents now believe, is what Malik did — & the couple, while apparently having carried out the deadliest jihadist attack on US soil since September 11, are not an anomaly.
In May of this year, two gunmen attacked a conference in Garland, Texas, which was hosting cartoons of the Prophet Mohammed designed to be offensive to some Muslims. Police suspect the attackers were self-radicalized jihadists.
And Wednesday's attackers were not even the first young US couple tempted by the movement. Earlier this year, 22-year-old Mohammad Oda Dakhlalla & 19-year-old Jaelyn Delshaun Young were arrested as they prepared to head to Syria.