The evolving crisis over Iran’s nuclear program has led the governments of the United States, Israel and other regional states to draw “red lines” that have shifted with time. Unfortunately, these red lines may be self-defeating in that their constant shifting gravely corrodes the credibility of those who set them—that is, credibility not only in the eyes of Iran but also in those of other important players, such as the Gulf states and other states in the region and beyond.

We define “red lines” as acts, activities or situations that, if carried out or arrived at, mandate corresponding actions in response. The purpose of setting red lines is twofold: to deter certain acts or activities; and to assess whether the situation is serious enough to warrant a particular reaction. Throughout the past decade, governments have set red lines such as “points of no return”, “technological thresholds”, “zones of immunity” and other specifically defined conditions; most such lines have been crossed at one point or another and no corresponding action to prevent Iran’s taking another step in advancing its nuclear program for military purposes has been forthcoming. Red lines have to be seen in the context of how the line-drawing party sees its interests in a given moment and its willingness, in case the line is crossed (politically, militarily, technologically and so on), to take the necessary measures to defend those interests.

The nature of the response can vary, of course, and the timing of the response depends on the sense of urgency with which the situation must be redressed. But redefining these lines while letting “old” lines pass without a response can create misunderstandings as to the seriousness of the line-drawing party, thereby eroding its credibility.

A deeper look at these issues is warranted, since the situation in Iran today is getting close to critical, and the drawing and application of red lines could have unintended and unwanted consequences. Two sets of red lines matter most: the U.S. and Israeli “red lines”, and “zones of immunity.”¹

The U.S. and Israeli red lines, as perceived by the outside world, have been defined as “reaching a nuclear capability” (Israel) and “breaking out” (the United States). The Israeli line is the vaguer of the two. It roughly means that Iran would have the capacity to produce nuclear weapons if it chose to do so—that is, it would have all the technical means and the knowhow to do it. The most difficult part of producing nuclear weapons is producing the necessary core materials—namely, the fissile materials. Iran has proven that it has the capacity to do so, in that it has enriched a considerable amount of uranium to the level of 3.5 percent and has even gone beyond that and enriched uranium to the level of 20 percent. Reaching the military level of 90 percent would be no problem for Iran; all that is lacking is the decision to go ahead and do it. From the technological view point, this red line has already been crossed.

The other red line, the “zone of immunity”, was defined by Israel as the point after which the Iranians could enrich uranium at their new enrichment facility at Fordo, near the city of Qom, without fear of attack because of its natural defenses (it is built inside a mountain). Because of the minimal dimensions of this facility and the limited number of centrifuges that can be installed there, the only realistic reason for its existence is the enrichment of uranium from low levels to military-grade ones. This, in a way, was the “smoking gun” that proved, by contradiction, that Iran had a military nuclear program; there was no other excuse for investing huge amounts of money in an installation with no viable peaceful purpose. Although the facility is not yet complete, enrichment has already been started there, and with the number of centrifuges already in operation Iran could enrich uranium up to military-grade levels. By setting this red line, Israel succeeded in bringing this specific issue to worldwide attention.

Although it seems simpler, the American red line is actually much more elusive. First there is the problem of defining “breakout”: One definition would be “starting to enrich beyond 20 percent.” However, wouldn’t “designing the nuclear explosive mechanism” be a reasonable alternative to this definition? This activity is uniquely related to nuclear weapons, while refinement to 20 percent is not. Iran could plausibly claim many reasons for enriching beyond 20 percent (such as medical purposes or naval propulsion), and it could also cite the fact that 20 percent enrichment of uranium has not been defined in a binding legal manner (other than in Security Council resolutions) as the limit for enrichment.

This second definition of a breakout, concerning the development of an explosive mechanism, has already been exceeded, since the United States admitted that Iran was actively engaged in the development of such a mechanism (at least until 2003). Furthermore, the IAEA, in its November 2011 report, detailed further information on the R&D work on the development of this mechanism; Iran could not, and did not, contradict this in any way other than a curt, flat denial.

Clearly,  the enrichment definition of a breakout is a very ineffective one. According to this definition, Iran could amass many tons of 3.5 percent and 20 percent enriched uranium, install thousands of advanced centrifuges that could achieve military-grade enrichments in a very short time, do this in the well-protected Fordo underground enrichment facility without crossing the breakout red line, and then wait for the opportunity or urgent need to break out. If this were the scenario, who would let the United States know that the breakout had actually occurred so that America could react in a timely manner? Given the inherent uncertainties in intelligence gathering and interpretation, can the United States depend absolutely on its intelligence services? This would probably necessitate a constant vigil and perpetual readiness of significant U.S. naval and aerial forces in or near the region.

But then comes a little-noticed item in the May 2012 IAEA report to its Board of Governors and to the UN Security Council, which found particles enriched up to 27 percent at Fordo. (The actual enrichment levels could have been even higher.) According to the report, “Iran indicated that the production of such particles ‘above the red value’ may happen for technical reasons beyond the operator’s control.” The IAEA is still investigating the matter.

Now, as a “thought experiment”, what would the situation be if this finding is the result of a real breakout? The first question is: When did the enrichment beyond 20 percent begin? The next issue would be to assess the timetable for the enrichment of a sufficient quantity for the first nuclear explosive core. And the next issue after that, of course, concerns what action should be taken. The perceived American red line has been crossed. No action? This was not a theoretical experiment. Even if this were not a breakout case, it is necessary to estimate the timetable if Iran broke out and rushed toward a nuclear weapon, comparing it with the IAEA (an extremely important source of information) timetable for investigating the matter.

What exactly, then, could trigger military action? Most probably it would not be the crossing of a red line. It would be a combination of several issues—technical, political, and, not least, public pressure. This last factor could work both ways, however.. Insisting on rigid definitions of red lines could be counterproductive, forcing governments under pressure either to take action or desist from doing so.

While for Israel the assessment and decision-making processes mainly concern nuclear issues, the U.S. leadership could probably be motivated by non-nuclear considerations as well. There are many possibilities that could trigger action, some stronger than others: evidence of the production of nuclear weapons, withdrawal from the NPT and the safeguards agreements, a nuclear test, non-nuclear incidents such as closing the Strait of Hormuz, global acts of aggression by Iran or its proxies, or some combination of the above. What will probably trigger military action against Iran (if it ever happens) is an intuitive assessment of the situation by the leadership of the United States or Israel.

Officials have recently begun using and discussing more openly the idea of red lines. Doing this could cause much more harm than good. If red lines are meant to deter, then not acting on them will reduce deterrence and strengthen Iran internally. Red lines tend to constrain those who draw them, putting their credibility at risk if they allow them to be crossed without response.

¹Editor’s Note: The issue of red lines is a subset of strategic issues and how one talks about such issues in public. For an examination of the perils of “tough talk” in general, see Shibley Telhami’s essay for The American Interest here.