“A feckless delusion that is never going to happen.” That’s how the current head of the CIA, John Brennan, described the possibility of the existence of an Islamic caliphate five years ago.

In a cruel piece of irony, the Islamic State, also known as ISIS, proclaimed the existence of such a caliphate precisely three years to the day after Brennan’s comments.

This caliphate has proven its staying power, becoming truly entrenched in Iraq and Syria. Furthermore, ISIS’ brand and its barbaric ideology have been disseminated far and wide. ISIS continues to carry out or inspire regular attacks abroad and has established affiliates in Saudi Arabia, Yemen, Algeria, the Sinai Peninsula, and many other parts of the Middle East and Africa.

Breaking ISIS is highly desirable, but there is no silver bullet to do so. Staving off any air of inevitability that ISIS is on the way to becoming a permanent, dominant regional force is key; and defeating the group militarily is naturally vital to these efforts. ISIS has had fantastic success in attracting foreign recruits, so cutting off its supply of new fighters is also crucial.

Turkey stepping up its efforts to block the flow of fighters via its territory has certainly boosted the war effort on this front. In a Heritage Foundation backgrounder, entitled “Combatting the ISIS Foreign Fighter Pipeline: A Global Approach,” my colleagues and I have made further practical suggestions on how best to combat this foreign fighter problem.

Despite some progress being made against ISIS, there is more that needs to be done. For example, over the weekend, ISIS was in the process of being kicked out of Fallujah, Iraq.

Yet this is only a pyrrhic victory if it means Fallujah ends up being occupied by Iran-backed Shia Popular Mobilization Units, as Sunnis in the area will never accept this status quo. Throw in inevitable abuse of Sunnis by these same forces, and it merely sets the scene for an eventual ISIS comeback.

There also appears to be little coherent strategy for resolving the mess in Libya, where ISIS has begun to shift its resources.

Therefore, a Senate hearing this week on the “Global Efforts to Defeat ISIS” is well timed, as key questions about how to handle the group remain unaddressed. That is not just the case when it comes to Iraq and Syria, either, as this war is now truly transnational.

ISIS’ latest overseas affiliate was just created in the Philippines. A French terrorist who swore loyalty to Abu Bakr al-Baghdadi murdered a French policeman and his partner earlier this month. Omar Mateen did the same during his massacre in Orlando. A global, coherent response is needed.

This is a tricky balancing act because the U.S. must also not develop tunnel vision. ISIS, as with al-Qaeda, is a manifestation of a broader challenge posed by the ideology of Islamism. Coming up with a long-term strategy for defeating a religiously-infused ideology that cuts across borders and exists in countries that the U.S. has limited scope to influence is no easy task. In its absence, however, the threat posed to us all can only endure.