Rewind to August 2017.

Islamist terrorists had just killed 16 people and injured another 137 in Barcelona and Cambrils. That attack had come hot on the heels of a wave of similar atrocities over the previous 2 1/2 years: Paris, London, Manchester, Stockholm, Berlin, Brussels, Nice and many others cities suffered significant losses of life as a result of plots either directed or inspired by the Islamic State of Iraq and al-Sham (ISIS).

It was an especially bleak time for Europe.

Then, the military campaign against the Islamic State began to take its toll. Adherents known to be planning attacks in Europe were targeted and killed in drone strikes. Raqqa, the Syrian base from which the Islamic State frequently planned atrocities in the West, fell. The flow of foreign recruits to replace the Islamic State’s fallen stopped as the thought of potentially dying for a group in retreat lost its appeal. In March 2019, the last Syrian town in the grip of the Islamic State was freed by coalition and Kurdish forces.

All the while, the pace of terrorist attacks in Europe also began to slow. And those that did occur became decreasingly spectacular. As the number of casualties diminished, the world largely moved on.

So few will have noticed — and fewer will remember — the Turkish gunman who injured five and killed three and injured five on a tram in Utrecht just six months ago. Or that, only four months ago, an Islamic State supporter exploded a nail bomb in downtown Lyon, France, injuring 13 passersby.

Before the rise of the Caliphate skewed our expectations about the level of security we can expect in Europe, those attacks would have been a big deal. Today, the size of the butcher’s bill needs to be pretty significant to get political and media attention. What was once abnormal is now considered a big yawn.

Yet speak to European security officials, and they will stress that the Islamic State threat remains persistent. This April, the then-head of Germany’s domestic intelligence agency stated that the Islamic State “can launch an attack in Germany any time.” The U.K. Counter Terrorism Policing’s senior national coordinator warned in June that, “the U.K. is still facing an unprecedented level of threat from terrorism.”

That should matter to Americans, too. Europe and the U.S. possess a shared value system. Millions of Americans live or vacation in Europe. American companies operate there, and the U.S. military has bases there. When terrorist attacks occur in Europe, Americans have been among the victims.

Clearly, the U.S. has an ongoing stake in European security. The U.S. has already performed a vital role by taking the lead in destroying the Caliphate that drew in so many Europeans. Now, it must resist the temptation to declare victory against the Islamic State and call it a day.

Instead, America must remain ready to deal with the group as it switches to an insurgency. The U.S. must also continue to help ensure that no new safe havens for terrorism emerge, working with local partners whenever that is appropriate.

It also must work with Europe on areas of disagreement. The thorny issue of what to do with European Islamic State fighters being detained by Kurds in northern Syria remains. Understandably, the U.S. wants Europe to take them back. Equally understandably, Europeans are wary, aware that the inadequacy of their terrorism legislation means that they will likely be unable to prosecute them and so will have to set a generation of Islamic State recruits free.

Still, these are kinks that need ironing out, not intractable problems. European and U.S. counterterrorism cooperation is strong. With the Caliphate in tatters and pressing challenges from Russia, Iran, China or North Korea coming to the fore, the trick is to ensure it remains so.