Deterring state sponsors of international terrorist organizations presents perhaps the most theoretically straightforward attempt to utilize deterrent strategies in the war on terrorism. Even those who are generally skeptical of deterrence being applied to terrorism believe the U.S. may be able to deter states from harboring or supporting terrorist organizations. Of the many elements that comprise a terrorist network, rogue regimes that support terrorists are the easiest to find. Assets of a rogue regime that can be targeted, such as the territory under its control or the lives of the ruling elite, are more apparent than the assets held by individual members of terrorist organizations. Efforts to dissuade states from forming relationships with terrorists also represent one of the critical aspects of the war on terrorism. Indeed, only days after the September 11 attacks, President Bush articulated what came to be known as the Bush Doctrine: “Any nation that continues to harbor or support terrorism will be regarded by the United States as a hostile regime.” 
The most salient concern for U.S. defense planners is the prospect of rogue states providing CBRN to a group such as al-Qaeda. The U.S. currently lists six countries as potential state sponsors of terrorism: Iran, Syria, North Korea, Cuba, and Sudan. In 2006 the U.S. State Department removed Libya because it apparently was assisting the U.S. in its war on terror. It appears that over the past few years, state sponsorship of terrorist organizations has waned. Libya, for example, has been cooperating with the U.S. to find Libyan members of al-Qaeda. Even more noteworthy, in December 2003, Colonel Muammar Qaddafi stated that the Libyan government would cease research and development of CBRN and would allow weapons inspectors to confirm its disarmamanent efforts. While the impetus for such positive steps are multifaceted, the U.S. success in ousting the Taliban from power and killing many of its members in Afghanistan has “served notice” to rogue regimes around the world that the U.S. is willing and able to destroy what rogue regimes value. Moreover, the possibility of Saddam Hussein acquiring CBRN and then passing these capabilities along to terrorists was a significant rationale for the U.S. invasion of Iraq. Many argue that Libya’s decision to dismantle its CBRN programs and other governments’ decisions to ratchet up the pressure they exert on al-Qaeda cells within their borders is at least partly due to a growing fear that U.S. military force might be used against regimes that continue to harbor terrorist organizations.  As Vice President Dick Cheney stated in the 2004 vice presidential debate with John Edwards, the Libyan decision to abandon its CBRN programs was one of the “great by-products” of U.S. actions in Iraq and Afghanistan. 
While it appears that U.S. military operations and legal actions since September 11 have established a deterrent mechanism against state sponsorship of terrorism, the threat of these initiatives remains a critical concern to policymakers. Osama bin Laden has voiced an interest in acquiring mass-casualty weapons and many analysts suggest that al-Qaeda would not hesitate to use CBRN weapons if it acquired these capabilities. To do so, however, terrorist groups need help, either by smuggling CBRN materials from poorly secured facilities or by developing relationships with foreign governments willing to transfer CBRN capabilities. Thus far, it appears that al-Qaeda’s pursuit of CBRN capabilities has been unsuccessful. In 2002, The New York Times reported that U.S. administration officials stated that “…analysis of suspected radioactive substances seized in Afghanistan has found nothing to prove that Osama bin Laden reached his decade-long goal of acquiring nuclear materials for a bomb.”  However, U.S. intelligence agencies suspect that Pakistani scientists gave al-Qaeda members information on how to construct a radiological weapon, or “dirty bomb.”  North Korea increased the fear of a state transferring weapons materials, when in 2003 it threatened to sell a quantity of plutonium to the highest bidder. Additionally, as Iran is on the cusp of developing nuclear capabilities, this scenario is becoming even more critical to U.S. defense planners.
Currently, the U.S. maintains a position of “calculated ambiguity” on how it will respond to a CBRN attack on its soil or against its interests abroad. The doctrine of calculated ambiguity garnered support when the Bush administration purportedly deterred Saddam Hussein from using biological or chemical weapons against U.S. forces during the first Gulf War in 1991. Secretary of State James Baker delivered a note to Iraq’s Foreign minister Tariq Aziz that cautioned Hussein that any use of these weapons could result in U.S. nuclear reprisals. The unclassified version of the 2002 National Security Presidential Directive (NSPD) 17 declares that the U.S. will reserve the right to respond with “overwhelming force” and keep open “all of its options” to a CBRN attack on the U.S., its interests, or its allies. In 2003, The Washington Times reported that the classified version of NSPD 17 made the willingness of the U.S. to respond with nuclear weapons to a CBRN attack more explicit.  Nevertheless, the U.S. is deliberately vague about its plans to respond to a CBRN attack. The strategic rationale for maintaining this ambiguity is to keep open a broad range of response options and approach potential events on a case-by-case basis. The vagueness of U.S. reprisal plans, however, does not support deterrence. The credibility of U.S. threats to retaliate suffers as a result of this ambiguity. While the use of language such as “overwhelming force” connotes a severe retaliation, this lack of clarity is not the best way to solidify the belief among terrorist-supporting regimes that their behavior puts them at severe risk. As one author notes, “Frequently, the bigger and more indiscriminate the threat, the less believable it is in the eyes of the target audience.” 
In order to establish a deterrent mechanism that will dissuade rogue states from supporting terrorist organizations, the U.S. must develop a strong declaratory policy that clearly communicates a threat of punishment for those states that provide CBRN materials to terrorists. Strategies for dealing with rogue states assisting terrorist organizations that are severe and target assets of value to the regime will best reinforce deterrent mechanisms. As Ian Lesser argues, for deterrence to be viable against rogue regimes, the threat of retaliation for supporting or sheltering terrorist organizations must be both “massive” and “personal to the leadership.”  The U.S. policy of calculated ambiguity reinforces many of the internationally held stereotypes of the U.S. that negatively affect its ability to establish a credible deterrent threat. By avoiding direct language, the U.S. appears irresolute, noncommittal, and perhaps overly sensitive to public opinion.
To create a credible deterrent threat, the U.S. must articulate a policy of regime change in those states that offer support to terrorist groups. Regimes that assist groups such as al-Qaeda, especially if this assistance is with acquiring CBRN capabilities, must know that they will be toppled and replaced if this support is identified. Specifically, the leadership of rogue regimes must be explicitly warned that they will be removed from power, suffer legal repercussions, or even be killed for maintaining ties with terrorist groups. Doing so would represent a meaningful threat of punishment to the leadership of rogue regimes. However, a stated policy of regime change presents numerous dilemmas. Most notably, sovereignty is still a revered concept in international relations. Engaging in a war to bring about regime change is acceptable in the international community only in instances of clear self-defense or through the decision of the United Nations Security Council.  Thus, in order to have international support to carry out a regime change, the U.S. would have to bring forth evidence that a particular state was responsible for transferring CBRN capabilities to a terrorist group that carried out an attack on the United States.
Making the case for regime change in Afghanistan was easy, as it was fairly clear to the international community that the U.S. was retaliating against a regime guilty of harboring and providing sanctuary to al-Qaeda. However, future attempts to gain international approval for regime change may be more difficult than they were in Afghanistan. The failure to garner widespread international support for the U.S. invasion of Iraq and the subsequent failure to find CBRN weapons will only serve to make the international community more skeptical of U.S.-led efforts to topple rogue regimes. Furthermore, the difficulties the U.S. has had in “winning the peace” in Iraq will decrease the credibility of U.S. threats to dismantle rogue regimes. The ruling elite in rogue regimes may be unconvinced of the willingness of the U.S. to topple a regime and engage in another nation-building effort. These arguments correspond with the often-heard suggestion that U.S. policy in Iraq has undermined its ability to fight the war on terror in other parts of the world.
In addition to articulating a policy of regime change, the U.S. must be more explicit in its capability and willingness to respond with nuclear weapons in the event of a CBRN attack. It remains uncertain whether the U.S. is likely to retaliate against an enemy that has used CBRN with either conventional or nuclear weapons. The psychological weight that the ultimate sanction of nuclear reprisals carries is critical in developing a meaningful deterrent threat against rogue regimes transferring CBRN capabilities to terrorists. As one author suggests, “The extremely high costs that a rogue state might suffer from nuclear retaliation should give even the most reckless of regimes pause before sharing a nuclear capability with terrorists.”  Threatening a massive conventional weapon response simply does not carry the same deterrent weight as the threat of nuclear reprisals. However, current U.S. nuclear capabilities prevent the U.S. from convincingly threatening nuclear retaliations against rogue regimes. The U.S. nuclear arsenal is too destructive to consider using, other than in retaliation to a nuclear attack. Because the U.S. nuclear arsenal consists primarily of weapons that have yields of hundreds of kilotons, U.S. threats to use nuclear weapons, especially in response to a biological or chemical weapon attack, are too incredible for rogue regime leaders to take seriously. Ambiguous threats about leaving the nuclear option open, when many enemies of the U.S. maintain little belief that the U.S. is willing to take action on these veiled threats, fails to support deterrence. The U.S. cannot credibly threaten nuclear reprisals against a CBRN attack because it is perceived the U.S. would not risk the extensive collateral damage and civilian casualties that would result from using the weapons in its current nuclear arsenal. Rogue regimes may rely on this moral and political reluctance by the U.S. when they consider transferring CBRN capabilities to terrorists.
In order for the nuclear option to be a credible part of the strategic menu, the U.S. must continue research on, and eventually development of, low yield nuclear weapons. Next generation “mini-nukes” could theoretically engage targets such as underground command and control bunkers, weapon labs, CBRN storage facilities, or even a presidential complex. As U.S. operations in Afghanistan and Iraq have illustrated, the war on terror will often present high-value targets that cannot be efficiently engaged with conventional munitions.
The development of mini-nukes and subsequent establishment of a declaratory policy of nuclear retaliation is a potentially divisive issue. First, the 1993 Spratt-Furse law bans any research and development of nuclear weapons that have yields of less than five kilotons. In May 2003 the House of Representatives adjusted the law, allowing research on low-yield nuclear weapons, but stated clearly that development and production of these weapons remains prohibited. Second, the mini-nuke debate polarizes the positions of “deterrence hawks” and “nonproliferation doves.” The production of mini-nukes blurs the line between nuclear and conventional munitions. It also creates a number of nuclear fallout concerns and undercuts U.S. counterproliferation efforts. For instance, the U.S. government, through the 1995 Nuclear Non-Proliferation Treaty (NPT) extension conference, assured that it would not use nor threaten the use of nuclear weapons against non-nuclear members of the NPT. Third, some scholars, notably Scott Sagan, argue that explicitly threatening nuclear retaliation could lead to a “commitment trap” whereby U.S. officials may feel that they must respond to an attack with nuclear weapons in order not to “lose face” domestically and internationally.  Finally, since WWII, a nuclear taboo has emerged in the U.S. and throughout much of the international community, whereby a normative prohibition stigmatizes the use of nuclear weapons as something only done by “bad states.” Therefore, some suggest that by producing nuclear weapons that are designed for non-nuclear targets, the U.S. may undermine the nuclear taboo.
A second important step in establishing a credible threat of retaliation involves CBRN weapon attribution. To effectively deter states from transferring CBRN materials to terrorists, the U.S. needs to develop its ability to identify the origin of the CBRN materials used in an attack against the U.S. The prospect of an unattributed CBRN attack poses a significant dilemma for establishing a deterrent mechanism. As Michael Levi argues, the U.S. must develop its ability to identify where the materials used in a CBRN attack originated. While intercepting weapon transfers before they occur should be the primary goal, the U.S. must have the technical ability to identify where CBRN materials came fromafter they have been detonated. As Levi points out, “If the United States can take that technical step, it can credibly assure its enemies that their transfer of weapons to terrorists will ultimately lead to their demise.”  Without adequate attribution ability, rogue regimes may be more inclined to transfer CBRN capabilities to a terrorist organization because they believe their identity may never be revealed. As long as rogue regimes believe the U.S. cannot detect where CBRN materials originated, U.S. threats of retaliation are somewhat hollow.
While continued efforts by the Defense Department to develop a more robust attribution system are vital, the infancy of this capability requires the U.S. to make a much more controversial threat in the near-term. It is not certain that the U.S. will always be able to garner enough forensic evidence from a CBRN attack to pinpoint the origins of these weapons after an attack has been carried out. There is a lingering question of how compelling forensic evidence must have to be in order to justify a massive retaliation against a state suspected of providing CBRN assistance to a terrorist organization. To establish an effective deterrent mechanism the answer to this question violates accepted legal standards. The U.S. will need to be prepared to retaliate on the basis of limited or imperfect information about the origins of weapons material. That is, the burden of proof will have to be relaxed. As a recent RAND report conjectures, in the event of a CBRN attack the U.S. may be forced to retaliate based upon “…reasonable evidence and would even make some assumptions about who is supporting terrorists in possession of WMD.” U.S. retaliation would have to come in spite of there being some doubt about where the CBRN capabilities actually originated. A U.S. decision to retaliate against state targets based on imperfect information will undoubtedly fan anti-American flames around the world and may even generate substantial domestic dissent. This is especially likely in light of the fact that the current White House toppled Saddam Hussein’s regime despite considerable questions about Iraq’s CBRN capabilities and development programs. The Kay Report has raised serious questions about the existence of ties between Iraq, al-Qaeda, and CBRN. 
Attribution difficulties present another, even more controversial, issue in terms of deterring states from transferring CBRN capabilities to terrorists. In addition to threatening massive retaliation and regime change against state supporters of terrorism, the U.S. must also develop a doctrine of retaliation against CBRN proliferators that do not adhere to international standards of securing CBRN materials. Even with the establishment of certain enticements through the Cooperative Threat Reduction (CTR) framework, or Nunn-Lugar legislation, a number of states have not developed the necessary safeguards to secure critical weapons materials. Pakistan and Russia, for example, continue to maintain fissile nuclear material facilities that are poorly secured. Moreover, the CTR and other nonproliferation efforts have failed to prevent Iran and North Korea from pursuing nuclear capabilities.  A comprehensive deterrent strategy would also threaten retaliation against those states that jeopardize international security by not conforming to international standards of safeguarding CBRN materials. That is, the “mere” crime of negligence and carelessness in overseeing CBRN materials must be punished. This is especially true in the event the U.S. cannot identify the origin of CBRN materials used in an attack. The U.S. must clearly communicate its willingness to severely punish those states that, because of mismanagement of CBRN, risk the loss or theft of critical materials from their storage facilities. Such a policy stance would be extremely contentious and may damage the relationship the U.S. has with a number of states. However, until CBRN attribution becomes certain, to establish a meaningful deterrent mechanism against states that knowingly transfer sensitive materials the U.S. must also threaten those states that do not adequately secure their CBRN materials.
The above discussion illustrates that establishing a deterrent mechanism, even in the theoretically most applicable case of deterring states from supporting terrorist organizations, would require the U.S. to adopt a number of controversial policies. To establish a meaningful deterrent mechanism against rogue regimes from supporting terrorist groups, the U.S. must take the following steps: (1) explicitly state that the U.S. will dismantle and destroy any regime guilty of supporting terrorist organizations, (2) increase research and development of mini-nukes and clearly communicate its willingness to retaliate with these weapons in the event of a CRBN attack, (3) develop a robust CBRN attribution system, and (4) warn states that do not maintain adequate security over CBRN materials and weapons that they will be punished in the event the U.S. is unable to identify the origins of a CBRN weapon used in an attack. Clearly, a number of these policies would be unpopular to many around the world. The uproar generated by President Chirac’s and Congressman Tancredo’s recent comments illustrates the potential problems with articulating a policy of massive retaliation and regime change. Moreover, the U.S. cannot make a credible threat of nuclear retaliation to a chemical or biological attack because its current nuclear arsenal is comprised mostly of weapons that are far too destructive. Making a credible threat becomes even more difficult when retaliation may have to be carried out on the basis of incomplete information about who exactly was responsible for giving a terrorist organization CBRN capabilities. With the current difficulties of CBRN attribution, and the fact that a number of states that do not directly support terrorist activities are negligent in securing CBRN materials, the ability of the U.S. to communicate a clear and believable retaliatory threat is further hampered. There exists too much opportunity at the present time for rogue regimes to transfer CBRN capabilities to terrorists without detection and therefore without fear of reprisals. Until these opportunities are reduced, or the U.S. is willing to communicate and carry out a number of potentially unpopular policy choices, effectively deterring states from forming any relationship with terrorist groups is unlikely.
A final problem with deterring state sponsorship of terrorism is unrelated to the myriad of issues that surface in regard to CBRN weapons. One of the biggest difficulties policymakers and analysts face is that state sponsorship of terrorism can include a wide spectrum of actions and degrees – ranging from very passive to very active. Even more problematic is that some states that maintain some degree of support for terrorist organizations are loosely considered U.S. allies.  For example, Pakistan’s intelligence service and military are known to sympathize with and at times directly support active Islamist terrorist groups in Kashmir. One such group, the al-Qaeda splinter group Jaish-e-Mohammed, has been linked to the December 2001 attack on the Indian Parliament and the 2002 murder of New York Times journalist Daniel Pearl. Therefore, to establish a credible deterrent mechanism, the U.S. would have to be willing to clearly signal to a number of its “allies” in regions such as the Middle East that it is prepared to carry out regime change or other drastic policy responses to even low-levels of passive support. Many countries, including purported U.S. allies in the war on terror, continue to “turn the other cheek” to terrorists operating within their borders because they simply do not believe or fear that the U.S. will punish them in a meaningful manner.
 See Congressional Research Service, “Terrorism: Near Eastern Groups and State Sponsors, 2002,” February 13, 2002, 37
 Quoted in David Ignatius, “A Gaddafi Cover-up,” The Washington Post, October 26, 2004
 Thom Shanker, “U.S. Analysts Find No Sign bin Laden had Nuclear Arms,” New York Times, February 26, 2002
 Owais Tohid, “Pakistan and its Proliferator,” Christian Science Monitor, February 6, 2004
 Nicholas Kralev, “Bush Signs Paper Allowing Nuclear Response,” Washington Times, January 31, 2003
 Avigdor Haselkorn, The Continuing Storm: Iraq, Poisonous Weapons, and Deterrence (New Haven: Yale University Press, 1999), 49
 Ian Lesser, “Countering the New Terrorism: Implications for Strategy,” in Countering the New Terrorism, ed. Ian Lesser, et. al. (Santa Monica: RAND, 1999), 129.
 Jasen Castillo, “Nuclear terrorism: Why Deterrence Still Matters,” Current History (December 2003): 427
 Scott Sagan, “The Commitment Trap: Why the United States Should Not Use Nuclear Threats to Deter Biological and Chemical Weapons Attacks,” International Security 24, no. 4 (Spring 2000): 85-115
 Michael Levi, “Deterring Nuclear Terrorism,” Issues in Science and Technology (Spring 2004).
 Davis and Jenkins, Deterrence and Influence in Counterterrorism, 40.
 See the testimony of David Kay before the House Permanent Select Committee on Intelligence, October 2, 2003,http://www.cia.gov/cia/public_affairs/speeches/2003/david_kay_10022003.html.
 Valerie Fotso, “Deterrence strategies may have come under fire due to nonproliferation efforts.” October 2012
 An anonymous reviewer brought this point to my attention.