European security officials are increasingly worried that Islamic State's reach will not fade even as the terror group loses its grip on Mosul and Raqqa, the twin capitals of its now-collapsing, self-declared caliphate.
Instead, they warn of an organization that has carefully reinvented itself in order to take the fight directly to the West, with Europe in the crosshairs.
"Despite the recent setback for the Islamic State on the battlefield, the group has reached a new level of capability," Manuel Navarrette, the head of Europol's European Counterterrorism Center, warned during a recent visit to Washington.
"ISIS has shown the capability to strike at will, at any time, at almost any chosen target," he said, using an acronym for the group.
Making the situation even more ominous, according to Navarrette, is that IS appears to be able to turn potential recruits into operatives faster than ever.
"We have never seen this before," he said.
"Most of them pledge allegiance just the day before," added European Union Counterterrorism Coordinator Gilles de Kerchove. "They mount attacks close to the places where they live."
This is a view shared by many European officials, some of whom have been taking their message directly to their counterparts in the U.S.
They describe a terror organization that has found a way to become more capable, leaving those responsible for stopping them with almost no room for error.
These officials point to recent attacks in Manchester, London and Paris, and attempted attacks in Belgium, as a sign of what is to come.
"ISIS is renewing itself, modernizing continuously," said Dick Schoof, the National Coordinator for Security and Counterterrorism for the Netherlands.
Growing online presence
And perhaps nowhere has IS's drive to evolve been more worrisome than online where, according to Schoof, the group's supporters and recruiters have been getting "more professional," moving beyond social media platforms like Twitter, Facebook and YouTube.
"They are even more effective in the dark web, in the hidden part of the internet," Schoof warned, building on what he described as already "strong and effective media apparatus and marketing apparatus."
Also worrisome for European security officials is that many of these online efforts appear to have increasingly downplayed IS's brand of extremist Islamist ideology and even Islam itself.
Rather, the "initial push factor," as some officials call it, has been heavy doses of peer pressure, with the ideology coming into play late in the process, if at all.
Such concerns seem to contrast with the steady warnings by U.S. officials of a looming "terror diaspora" in which foreign fighters who once flocked to the Islamic State turn their wrath on their homelands, especially in the West.
"The so-called caliphate will be crushed," former FBI Director James Comey told U.S. lawmakers in September 2016. "The challenge will be that through the fingers of that crush are going to come hundreds and hundreds of very dangerous people."
While not trying to minimize the dangers, European counterterrorism officials say such fears have yet to manifest in their countries.
"The more I look at this, the more I believe we won't have a massive return. We won't have a high number of returnees," said EU Counterterrorism Coordinator de Kerchove.
European officials say of the approximately 5,000 citizens and residents who traveled to Syria and Iraq to join Islamic State, about half are believed to be dead. And they think many others will fight for IS in Iraq and Syria until the very end, or leave for new territories outside the West in which they can fight.
"Most of them will be killed, I think," de Kerchove said, further describing efforts by IS to sneak fighters into Europe with migrants as "not very significant."
There also is high confidence that the vast majority of Europeans who went to fight with IS are now known to the various intelligence agencies, their identities entered into the EU's Schengen Information System, making them available to local police and border agencies.
But there are concerns that despite the progress, Europe remains vulnerable.
"Some foreign fighters are still coming back," one European diplomatic official told VOA on condition of anonymity, given the sensitivity of the intelligence.
And many more already have successfully returned.
The EU estimates as many as 1,400 foreign fighters, nearly a third of those who left to fight, are already back in their countries of origin, although at least some of them are thought to be women and children who accompanied would-be jihadists.
"This is one of the main factors that helps explain the wave of attacks, both thwarted and successful, that have hit Europe," said Seamus Hughes, deputy director of the George Washington University Program on Extremism, during a congressional hearing Tuesday.
European officials say many of the plots have been foiled, and studies note there has been a decrease in the number of attacks involving foreign fighters following the November 2015 attacks on Paris.
"Law enforcement, intelligence officials in the West have been very good at trying to disrupt attacks by the foreign fighters," according to Kim Cragin, a senior research fellow in counterterrorism in the National Defense University's Center for Complex Operations.
"The question is whether or not these law enforcement officials can actually sustain this level of effort."