As the 9/11 Commission Report highlighted, following a “no sanctuary” policy against terrorist groups is not always viable. Photograph by Alex Wong / Getty

In the summer of 1985, Ronald Reagan, concerned about a spike in the number of international terrorist attacks from 1983 to 1985, delivered a speech on the subject before the American Bar Association. He offered a simple prescription: “There can be no place on earth left where it is safe for these monsters to rest or train or practice their cruel and deadly skills. We must act together, or unilaterally if necessary, to ensure that terrorists have no sanctuary anywhere.”

More than a decade later, in May, 1998, a few months before the embassy bombings in Kenya and Tanzania, as the threat grew from Osama bin Laden’s Al Qaeda network, which was then safely ensconced in Afghanistan under the protection of the Taliban, Bill Clinton spoke at the Naval Academy and promised “to work with other nations to eliminate terrorist sanctuaries overseas.”

Clinton’s top counterterrorism official, Richard Clarke, fashioned a proposal he called “Delenda” (Latin for “must be destroyed”) to “immediately eliminate any significant threat to Americans” by denying bin Laden his Afghan protectorate. Clarke remained at the White House at the beginning of the Bush Administration, and proposed much the same strategy in the months before the September 11th attacks.

But neither Reagan, nor Clinton, nor Bush made the “no sanctuary” policy a centerpiece of their national-security strategy. The idea of invading Afghanistan, absent a serious attack on American soil, seemed unreasonable. The authors of the 9/11 Commission Report wrote, in 2004, “Since we believe that both President Clinton and President Bush were genuinely concerned about the danger posed by al Qaeda, approaches involving more direct intervention against the sanctuary in Afghanistan apparently must have seemed—if they were considered at all—to be disproportionate to the threat.” The report added, “Insight for the future is thus not easy to apply in practice. It is hardest to mount a major effort while a problem still seems minor. Once the danger has fully materialized, evident to all, mobilizing action is easier—but it then may be too late.”

“No sanctuaries” became one of the central recommendations of the 9/11 Commission, which repeatedly warned that Al Qaeda, and groups like it, should never again be allowed to operate in a safe haven where they have “the operational space to gather and sift recruits,” especially in failed states. “If, for example, Iraq becomes a failed state, it will go to the top of the list of places that are breeding grounds for attacks against Americans at home,” the report noted. This was the year after the Bush Administration invaded Iraq, and three years into the war in Afghanistan, about which the report’s authors added, “Similarly, if we are paying insufficient attention to Afghanistan, the rule of the Taliban or warlords and narcotraffickers may reemerge and its countryside could once again offer refuge to al Qaeda, or its successor.”

Eleven years after the Commission’s report, ISIS is safely operating in a sanctuary the size of Indiana and, with the notable exception of Lindsey Graham, neither President Obama nor any Presidential candidate, whether Republican or Democrat, has put forward a detailed plan that would uproot ISIS from the territory it controls across Iraq and Syria. Even Jeb Bush, who on Wednesday said more American ground troops were needed to fight ISIS, did not propose a massive ground invasion, or not forthrightly. Like all of the candidates, he was disappointingly vague about how the military could solve the problem.

Indeed, President Obama is about the only public official to have honestly explained, in the days since the Paris attacks, why a quick end to ISIS’s sanctuary is not immediately possible. He mentioned those who “suggested that we should put large numbers of U.S. troops on the ground,” and then said,

Keep in mind that we have the finest military in the world and we have the finest military minds in the world, and I’ve been meeting with them intensively for years now, discussing these various options, and it is not just my view but the view of my closest military and civilian advisors that that would be a mistake—not because our military could not march into Mosul or Raqqa or Ramadi and temporarily clear out ISIL, but because we would see a repetition of what we’ve seen before, which is, if you do not have local populations that are committed to inclusive governance and who are pushing back against ideological extremes, that they resurface—unless we’re prepared to have a permanent occupation of these countries.

And let’s assume that we were to send fifty thousand troops into Syria. What happens when there’s a terrorist attack generated from Yemen? Do we then send more troops into there? Or Libya, perhaps? Or if there’s a terrorist network that’s operating anywhere else—in North Africa, or in Southeast Asia? So a strategy has to be one that can be sustained.

In some quarters, Obama’s realism about defeating ISIS has been taken as defeatism. He is, the argument goes, clinging stubbornly to a strategy meant to gradually reduce the group’s footprint, while simultaneously pursing broader diplomatic goals in Iraq (convincing the Shiite-dominated government to make disfranchised Sunnis feel that they have a voice) and Syria (ending Assad’s reign and moving toward a transitional government) that he insists are the real roots of ISIS’s growth. His willingness, especially in the wake of a horrific attack, to withstand the pressure to offer a swift military solution is impressive.

And Obama has some surprisingly good company. “Once you take ’em, you own ’em,” former New Jersey governor Thomas Kean, who was the chairman of the 9/11 Commission, told me on Wednesday, after Jeb Bush’s speech. “Then you get called ‘the Crusaders’ and all that. We’ve put too much reliance on the military to the exclusion of other things. We have a whole realm of other tools at our disposal.”

That kind of careful response can be emotionally unsatisfying. At the same time, anyone offering an easy plan to defeat ISIS fast and on the cheap should be met with extreme skepticism. But one lesson of Iraq (and Libya) is that wars are always more complicated than they sound and often create new sanctuaries—which then also, somehow, must be destroyed.