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Domestic terrorist Timothy McVeigh, the man who killed 168 people in the Oklahoma City bombing of a federal building in 1995.

(AP Photo/David Longstreath)

Max Abrahms is a fellow in the political science department at Johns Hopkins, where he teaches courses on terrorism and international relations theory.

By Max Abrahms, Foreign Policy

As law enforcement and counterterrorism officials continue the massive manhunt and investigation into the twin bombings in Boston, there's speculation as to whether the attacks were the work of "homegrown" actors, that is, terrorists residing in the country.

Right-wing extremists are possible culprits. After all, they like to come out of the woodwork in the month of April. Recall the Waco siege ended on April 19, 1993. Timothy McVeigh honored that ignominious day by blowing up the Alfred P. Murrah Federal Building in downtown Oklahoma City two years later, inspiring the Columbine high school students to go ballistic on April 20, 1999.

Alternatively, al Qaeda-inspired terrorists may be responsible for the Boston massacre. For years now, the leadership has called on its foot-soldiers to strike the homeland from within rather than to partake in risky operations abroad.

When Americans think of terrorism, they naturally think of the international variety (in which the perpetrators are not from the target country). The United States has historically been the leading target of international terrorism, while incurring relatively little bloodshed at home. Embassies -- not sporting events -- have been the preferred target of terrorists looking to take American lives. For this reason, terrorism datasets such as the U.S. State Department's Country Reports on Terrorism and ITERATE have historically been limited to incidents of international terrorism, ignoring domestic attacks entirely. Yet this national experience is actually anomalous. Each year, domestic terrorists kill far more people across the globe than do international terrorists.

Why do domestic groups have superior killing power? There is power in numbers. And unlike international terrorist groups, domestic actors can hope to draw supporters from local populations, helping to challenge government policy. But do the Boston attacks herald a newfound wave of domestic terrorism? Will they attract enough supporters to test Washington or our fundamental way of life? Not a chance. And here's why.

Simply put, too few terrorists exist within our borders to pose an existential problem. The policy community is fond of saying how lone wolf terrorists are hardest to stop. This is no doubt true. But left unsaid is they are also inherently weak, incapable of mounting complex operations. Lone wolves like Faizal Shazhad and the underwear bomber have tended to be quite feckless. Timothy McVeigh did manage to kill 168 people in one shot. But his first bombing was his last. Smaller groups may be able to launch such attacks from time to time, but are ultimately unable to sustain a proper campaign.

The United States is relatively terrorist-free for several reasons. For starters, democratic channels enable citizens to peacefully address their political problems. Without question, the aggrieved in the United States are better off going to the ballot box than planting IEDs. Indeed, American minorities are pretty happy here, including Muslim Americans. This contentment translates into moderation in not only their tactics, but also in their political preferences. Domestic terrorist groups are hence unattractive political outlets.

Evidence suggests that terrorism's appeal may actually be on the wane worldwide. Across countries, people have turned to terrorism when it seemed to offer the best chances of achieving their demands. But with so few recent terrorist victories, the tactic no longer holds the promise of profitable political change.

Take al Qaeda, the most salient example. Osama bin Laden stated in his 1996 and 1998 fatwas that the purpose of the violence was fourfold: 1) to eject the United States from the Persian Gulf; 2) to end U.S. support for pro-Western apostate regimes; 3) to sever U.S.-Israeli relations; and 4) to end "Crusader" wars that kill countless Muslims.

In response to 9/11, though, the George W. Bush administration did the exact opposite. It increased U.S. military personnel in the Gulf by a factor of 15. It strengthened U.S. relations with pro-Western leaders in Egypt, Pakistan, and Saudi Arabia, all in the name of counterterrorism. The U.S.-Israeli special relationship blossomed, with President Bush granting Prime Minister Ariel Sharon unprecedented leeway to occupy the West Bank. And, of course, 9/11 led to battles throughout the world resulting in greater -- not fewer -- Muslim deaths.

The most fearsome terrorist group in world history has achieved none of its political demands. Al Qaeda's pitiful political record stands in stark contrast to the Arab Spring, in which nonviolent movements toppled governments from Egypt to Tunisia, in just a fraction of the time.

Research shows that terrorism is not just correlated with political failure -- it actually causes it. And that's even after taking into account the strength of the perpetrators, government opposition, and other relevant confounds. Terrorism is a losing political tactic for a simple reason -- it is deeply unpopular among potential supporters. In the parlance of political science, terrorism carries prohibitive "audience costs." Rather than attracting supporters, terrorism actually reduces them, starving the organization of essential manpower. Ironically, the best antidote to terrorism is terrorism itself -- not hardening targets or invading foreign countries.

The lesson to terrorists is becoming ever clearer. Lay down your arms and you stand a better chance of prevailing politically. Such thinking is already firmly entrenched in Boston and the U.S. polity broadly, reducing the potential of a homegrown threat from ever really materializing. Of course this assumes the terrorists are rational political actors, but that's for another day.