The killing of an individual foreigner overseas, if carried out for a political or policy purpose by either a nonstate actor or clandestine agents of a state, is an act of international terrorism. At least that is how U.S. law defines it, for purposes such as the State Department's annual reports on terrorism. This form of terrorism is part of what put Iran on the list of state sponsors of terrorism. Through the 1980s and into the 1990s, the Iranian regime perpetrated numerous assassinations of exiled Iranian political dissidents, in Europe as well as in other countries of southwest Asia. The Iranians effectively ended this assassination campaign about a decade and a half ago, largely to improve relations with the European countries on whose soil many of the assassinations occurred and perhaps also because by then Iran had bumped off nearly all of the people on its hit list. We should assume, however, that Iran retains the capability to assassinate far-flung targets again, and that it would consider doing so if searching for ways to strike back at adversaries that are striking it.

Iran itself has been a victim of this form of terrorist violence. This has included some instances, such as the killing of Iranian diplomats in Afghanistan, in which Iranian interests have paralleled those of the United States. It has included during the past two years the killing in Iran of several nuclear scientists, the most recent of whom died this week from an explosive placed on his vehicle. Actions are more important than nomenclature, so if you prefer not to apply the T-word to these killings then just imagine what the reaction would be if something similar were occurring in the United States. Imagine the response if even just one scientist (let alone four or five) who was employed, say, at one of the U.S. national laboratories had been been similarly assassinated and a foreign hand was suspected. There would be screams of “act of war” and the U.S. president would be hard-pressed to hold back impulses to strike back forcefully. Now put yourselves in the Iranians' place. Not only do they face the serial assassination of their scientists, but they face it amid an environment filled with numerous other indications of foreign hostility, including the economic warfare, the saber rattling and the contest among American politicians to see who can shoot the most rhetorical venom at Iran. From this perspective, aptly described by Vali Nasr, it should hardly be surprising if Iran strikes back while it sees more reason than ever before to develop a nuclear weapon in the hope of deterring U.S.-led aggressiveness.

I don't know, of course, who is responsible for the assassinations of the scientists. I do not believe my own country is, and Secretary of State Clinton has explicitly denied “any United States involvement in any kind of act of violence inside Iran.” Although over the last thirty years the United States has edged away from the strict prohibition on assassination embodied in Executive Order 12333, we Americans are still morally (and esthetically) squeamish enough about such things that the kind of hit job that took place this week on a north Tehran street doesn't seem to be our thing. We assassinate people, but in addition to euphemizing the act by calling it “targeted killing,” we limit the targets to people we are convinced are themselves terrorists, not scientists or something else. We also use means that we can think of as “war,” preferably means that can be employed from several thousand feet in the air so we don't get too close to the bloody reality. The one time we did get close to it, last May, we still used military means, and that was to eliminate the most notorious terrorist in the world.

My hunch about responsibility for the killing of the Iranian scientists is similar to that of Trita Parsi, who says the assassination “was likely conducted by a regional actor who prefers a military confrontation with Iran over a compromise that would permit Iran to retain nuclear enrichment capabilities, even if it doesn’t build a bomb.” The trouble for the United States is that because it so obsequiously does the bidding of the regional actor in question, it is seen as responsible for anything that actor does and can be expected to share in any resulting opprobrium or retaliation for what that actor does. This gets back to Iran's continued presumed capacity for making assassinations a tit-for-tat business. Do not be surprised if it endeavors to do exactly that, although Tehran will pick its targets, timing and methods carefully to achieve a degree of deniability. The last confirmed official Iranian involvement in committing a terrorist act that killed Americans—the bombing of Khobar Towers in Saudi Arabia in 1996—left tracks well enough covered that it took years of investigation to determine the Iranian role. Possibly the caper last year involving the DEA informant and the used-car salesman from Texas was intended as a reprisal for earlier assassinations of Iranian scientists, but the public story of that supposed plot is still so murky that any Iranian role can hardly be considered “confirmed.”

A further tragedy in all of this is that it is a stretch, to put it mildly, to think that murdering some scientists would delay the oh-so-feared Iranian nuclear weapon, as if the only plans and knowledge useful to the program resided in the heads of the murdered men. And this is entirely in addition to the moral dimension of what has taken place. What do we know about Mostafa Ahmadi Roshan that makes him any more worthy of being a victim of assassination than counterpart scientists in the United States or elsewhere would be?

The proper U.S. response to all this is to pursue—vigorously—negotiations with Iran, with the starting point being the most recent Iranian proposal for a new round of talks with the P5+1. That is the only way out of the larger spiral of mutually reinforcing hostility of which the assassinations are only a part. And if, as Parsi suggests, the most recent act of terrorism was intended at least partly to scuttle such talks, that is all the more reason to negotiate in earnest. To do otherwise would be, to use a hackneyed phrase, a victory for the terrorists.