Once upon a time the big threat to civilization was al-Qaeda. But today it is ISIS, alternatively known as the Islamic State, ISIL, or Daesh. Transcending their existence as actual physical entities, the names or acronyms have become metaphors for terrorist attacks, striking fear in the hearts of the people and enabling the political class in Europe and the United States to grow government in response. At the Republican National Convention, presidential candidate Donald Trump vowed to destroy ISIS—and the Democrats led by Hillary Clinton will probably follow suit. But can it be done? Or, more to the point, how does one go about doing it? How will Trump and Clinton keep their promises to keep Americans safe from Islamic radicals?

What we call terrorism is a tactic used by groups that are essentially political. You can find it in Tacitus, read about it in the accounts of 19th-century anarchists, and consider how it evolved in modern times, starting with the European leftist groups in the 1970s and then migrating to the Middle East. Today terrorism and Islamic radicalism are closely linked, but it is important to remember that it was not always so. What we refer to as terror enables a weaker party to demoralize and even threaten the stability of a nominally much stronger ruling authority.

The United States distinguishes terrorism from mass murder. In the U.S. code, it describes terrorism as “acts dangerous to human life that violate federal or state law” that “appear intended (i) to intimidate or coerce a civilian population; (ii) to influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination or kidnapping.” 

So terrorism narrowly construed is an action intended to destabilize the political status quo so as to influence or pervert government decision making. But the definition is somewhat anachronistic. If one moves beyond the legal language, several categories of mass murder might plausibly be regarded as “terroristic” because they inevitably create fear when they include the indiscriminate taking of human life, particularly in situations where people going about their daily lives should normally feel secure. In so doing, whether their prime objective is political or not, they produce a reaction from the government, generally in the form of new laws that enhance the power of the state—which in turn can make the citizenry increasingly suspicious of the authorities.

Three common perpetrators of mass murder are the mentally ill, revenge seekers, and those motivated by an ideology to kill those they define as enemies. The three categories can sometimes overlap, of course. And the weapons they choose are most often guns, sometimes bombs, and more rarely instruments that are not usually associated with intentional killing, to include moving vehicles.

Consider as examples the profiles of eight of the most widely reported recent multiple killings in Europe and the United States, all of which have been described by the media as terrorist acts. The most recent took place in Munich last week, where ten people died. The perpetrator was a mentally deranged German born gunman of Iranian descent who was obsessed with mass killing itself. That was preceded by another attack in Bavaria by an ax- and knife-wielding Afghan refugee on a train, while a Bastille Day attack in Nice by a French citizen of Tunisian descent used a truck to kill 84 during the same week. Both of the latter attacks were reportedly inspired by ISIS.

A March attack on a Brussels airport and a metro station by five Belgian-born citizens of Arab extraction killed 32 using guns and bombs. In November of last year seven Belgian and French citizens of Arab extraction used guns and bombs to kill 130 at restaurants, a theater, and sports facilities in Paris. One additional attacker was a refugee and still another was unidentified. Both attacks were reportedly inspired by ISIS. In January of the same year, the famous attack on Charlie Hebdo took place, also in Paris, with two French citizens of Algerian extraction shooting 13 people and claiming to be inspired by al-Qaeda.

Here in the United States there have recently been two attacks. In June, 50 Americans were killed in a nightclub in Orlando in a shooting carried out by an American citizen born to Afghan refugees; he claimed allegiance to ISIS but has been regarded as having mental problems. In December 2015, 14 died in San Bernardino at the hands of a Chicago-born gunman of Pakistani descent and his Pakistan-born wife, both of whom pledged allegiance to ISIS.

If Donald and Hillary really want to make us safe and actually intend to take steps to do so, what can or should be done to address each category of mass killer and each type of weapon? The convenient response by Hillary Clinton, which she is already offering, is gun control. But any analysis of the recent incidents suggests that it will always be easy to obtain weapons, even in the tightly-controlled Western European environment. In Europe, suppliers are frequently able to connect with those interested in acquiring handguns or rifles. Many of the weapons originate in the Balkans (particularly Kosovo, where they are relatively available) and make their way to the west. Likewise in the United States new laws would not eliminate the hundreds of millions of weapons already in private hands. So gun control, which seems to some to be a simple and affordable solution, would most likely accomplish little or nothing.

Another promising approach, favored by Donald Trump, connects terror to Islam. He has proposed banning the entry of all Muslims or at least those residents from a handful of countries where metastasizing violence promoted by Islamic radicals is prevalent. He has also suggested that there might be “extreme vetting” of citizens from European countries subject to repeated terrorist attacks. The president has considerable authority to initiate such limitations on visa exemption or issuance, though any filtering based purely on religion rather than nationality would no doubt run into legal problems.

Some might plausibly argue that if Pakistanis and Afghans had been forbidden entry into the U.S., Orlando and San Bernardino would not have occurred. But it is difficult to imagine ruling out certain nationalities as potential immigrants as a sustainable policy. It would be far better to develop investigative procedures to weed out potential problems before they are granted visas, but no one is proposing that.

Likewise if North African Arabs had been blocked from residency in Europe, most of the six incidents cited above quite plausibly would not have occurred. Still nearly all of the perpetrators were actually born in Europe or were naturalized citizens; only two were refugees. This suggests that Europe already has large Muslim minorities that are infected by the radicalism bug, which in the U.S. is referred to as “homegrown extremism,” so closing the immigration door now might have little effect. It is neither practical nor politically imaginable that existing Muslim populations should be expelled, leaving one with no better options than increased police surveillance.  

Clinton, unlike Trump, appears to favor the current lax visa entry procedures, possibly because she was recently involved in their implementation. But there is a reasonable approach that falls somewhere in between exclusion and an open door: restrict visas for applicants who cannot be thoroughly vetted through existing procedures. Whether either candidate would embrace such fine tuning of the obviously broken system is unclear. There also might be considerable interference from a Congress that would seek to punish some countries when passing enabling legislation and providing funding.

So you can’t stop the guns and it is difficult to create a rational basis for blocking new immigrants or visitors, but the real problem is identifying the mentally disturbed and those influenced by groups like ISIS, who together have carried out nearly all the multiple victim, terrorist-style attacks in the past five years. The United States could destroy ISIS’s caliphate physically from the air, at a cost of possibly tens of thousands of civilian casualties, but it cannot eliminate the group’s effective internet-based propaganda machine. And when ISIS relies on “lone wolf” proxies or independent cells to stage attacks, the nation’s security services are increasingly unable to identify affiliates actually organized and directed by ISIS that would be discoverable and susceptible to being dismantled (if they exist).

Even if ISIS has no physical Caliphate, it will persist online and be accessible to those who seek it out. And it will undoubtedly someday be succeeded by new, even more radical groups with updated messages for the disaffected. U.S. law enforcement attempts to identify those individuals who try to interact with extremist websites and then uses informants to develop criminal cases against them, but it is a process that probably creates more radicalization than it prevents. And as for the mentally disturbed, they only surface when they are reported to authorities by a family member or health care provider, so there is little that one can do to prevent incidents besides encouraging such reporting.

So no matter what the candidates pledge to do, the options available to our next president to deal with ISIS and other terrorism are not very promising. Getting rid of guns is a non-starter and deporting birthright citizens would be both illegal and present practical difficulties. Keeping dangerous visitors out would be highly desirable but it is probably beyond the ability of government bureaucrats to develop and manage such a program successfully. Meanwhile the FBI and NSA read emails, listen in on phones, and react. I would imagine that a post-election review of national security will have all parties throwing up their hands in frustration over the paucity of reasonable options. The new president will likely pretty much come down in support of the status quo.

Philip Giraldi, a former CIA officer, is executive director of the Council for the National Interest.