Booster or Brakeman? Explaining the Changing Pattern of US Arms Control Policy

by Dr. Florian Böller

Within two years of his presidency, Donald Trump cancelled or threatened to cancel several important international treaties and agreements, including the Paris Climate Accord, the Trans-Pacific Partnership, the Iran Nuclear Deal, and, most recently, the Intermediate Nuclear Forces Treaty (INF). In fact, withdrawing from international commitments represents a core element of the president’s ‘America First’ doctrine. To be sure, skepticism against binding treaties and putting national interests first are recurring themes of US politics and were not invented by Trump. President Clinton, for example, could not convince a majority in the Senate to ratify the Comprehensive Test Ban Treaty (CTBT) in 1999, and President Bush withdrew from the Antiballistic Missile Treaty (ABM) in 2002. On the other hand, the US boosted international institutions in various policy fields including arms control, for example with the Strategic Arms Limitations Talks (SALT I & II) during the Cold War, or, more recently, under President Obama’s leadership with the New Strategic Arms Reduction (START) Treaty of 2010.

President Donald Trump delivers remarks on the Iran Strategy in the Diplomatic Reception Room
at the White House on October 13, 2017. (Official White House Photo by D. Myles Cullen)

My new research project analyzes the conditions that explain this shifting pattern ranging from a ‘brakeman’ to a ‘booster’ role in the field of international treaties and agreements. More specifically, I examine the politics of US arms control policy by connecting insights from domestic politics, in particular the role of partisanship and ideology, and international relations, which highlights the perception of threats and of reciprocity and trust. In this blogpost, I introduce a novel dataset and employ the method of fuzzy-set Qualitative Comparative Analysis (fsQCA) to evaluate 26 cases of US decisions on international arms control treaties and agreements from 1963 to 2018 (for background information on the treaties, see here).

While scholars have investigated the domestic side of US treaty politics before (see i.a. Krutz/Peake 2009), a comprehensive answer to explain the shifting patterns is still missing. In addition, Trump’s ‘America First’ policy threatens core elements of the traditional US leadership role—such as the commitment to international agreements. Identifying the conditions that contribute to Trump’s treaty politics is therefore relevant for the transatlantic liberal order.

1. Method

Fuzzy-set QCA is a burgeoning method in the social sciences (see Siewert 2017; Mello 2014; Böller/Müller 2018). Based on Boolean algebra, a set of cases is analyzed to identify necessary and sufficient conditions for an expected outcome. Rather than calculating the relative effect of variables, specific (sets of) conditions can lead to the same outcome. At the same time, the absence of an outcome may be connected to different conditions. Many phenomena in IR entail such complex combinations of causal factors. This is why fsQCA is particularly suited to investigate the question of US treaty politics. Here, one can expect that events are caused by varying domestic and international conditions. FsQCA allows to study this topic in a case-oriented and comparative approach.

In the following fsQCA, the 26 cases are assigned with membership scores along their specific conditions on a four-value set. Based on the criteria outlined below, a case is either ‘fully in’ (1), ‘more in than out’ (0.75), ‘more out than in’ (0.25), or ‘fully out’ (0) a given set of outcome and conditions. The calibration of sets needs to rely on theoretical knowledge and uses qualitative as well as quantitative indicators.

2. Conditions Driving the Politics of Arms Control

The US Constitution grants the president a preeminent role in negotiating international agreements. However, a two-thirds majority in the Senate is necessary to ratify international treaties. In recent years, presidents sought to circumvent this threshold by concluding executive agreements instead of treaties, which have relatively similar impact but lack the domestic commitment. Both joining as well as withdrawing from treaties is oftentimes highly contested within and between parties, among voters and between the president and Congress.

International conditions affect US treaty politics, too. Neorealists, for example, hold that states focus on threats to their security interests and seek to advance national interests. Institutionalist approaches on the other hand highlight the possibility of positive-sum games and claim that actors enter regimes if they perceive the partner as trustworthy and the commitments as reciprocal and fair.

Drawing from both the domestic and the international context, I consider four conditions that explain whether the US adopts a brakeman position (i.e. withdraws or rejects treaties) or a booster position (i.e. supports and renews treaties) (see Table 1). First, I argue that presidents and their partisanship matter. I suppose that conservative Republican presidents are more likely to withdraw from arms control treaties than liberal Democratic presidents are. Second, I take the influence of treaty skeptics in the US Senate into account. Here, I focus on Republican Senators and their ideological position, since this group has historically been most skeptical of international obligations. Third, to grasp the international threat environment, I use the percentage change in defense expenditures as an indicator. The underlying (neorealist) assumption is that rational actors evaluate risks and react with higher spending to more threatening environments. Higher threat levels consequently make international cooperation more difficult. Fourth, whether domestic actors perceive treaties as fair and reciprocal is also relevant. I hypothesize that multilateral settings increase complexity, complicate verification, and thus decrease the level of trust towards the cooperation partners. Furthermore, if the US perceives that cooperation partners receive relative gains from treaties or violate commitments, the rejection of or withdrawal from treaties is the outcome.

Table 1: Outcome and Conditions
Notes: P = ideology based on DW-Nominate Scores (first dimension, see Lewis et al. 2019). C = average ideology of Republican Senators*number of seats. I = annual change of defense expenditure in percentage (see SIPRI 2018). B, T = qualitative assessment.

3. Analysis

The fsQCA calculation for this dataset was performed with R, a software environment for statistical computing, and the QCA package for R, version 3.3 (Dușa 2019). I note for the conjunction of conditions (logical AND) ‘*’, for disjunctions (logical OR) ‘+’, and the negation ‘~’. The analysis starts by looking for necessary conditions. In this case, no condition exceeds the expected threshold (full documentation of fsQCA and replication data are available upon request).

The next step is to compile a truth table which informs of all combinations of conditions and evaluates whether each set of conditions is sufficient for the outcome. For this first analysis, I focus on the “parsimonious solution”, which also includes logical remainers (combination of conditions without empirical cases) in the minimization procedure.

Table 2: Combined Truth Table
Note: Con = Consistency; PRI: Proportional Reduction in Inconsistency; threshold 0.8 of Con;
row 8 not sufficient for non-outcome because of deviant case SALT II (marked with *).

The truth table algorithm reveals two paths for a brakeman position. First, the combination of a conservative president and the perception of a lack of reciprocity is sufficient for the outcome of the US acting as a brakeman (P*T → B). This combination accounts for the decisions to withdraw from the Iran Nuclear Deal, the INF Treaty in 2018 and from the ABM Treaty in 2002 as well as for the brakeman position on Cluster Munition and the Treaty on Nuclear Weapons Prohibition. Second, a hostile international environment in combination with the perception of unfavorable ‘tit for tat’ also produces this outcome (I*T → B), which explains the cases of the failure to ratify the CTBT as well as the decisions on the Cluster Munitions and the ABM Treaty. The solution term is consistent and can account for 6 out of 9 brakeman cases (see Table 3).

To explain the 17 cases in which the US favored international treaties and acted as a booster for arms control, the analysis identifies four paths. First, Republican presidents concluded several important agreements during the Cold War (Seabed Treaty, SALT I, BWC, INF, MTCR) and under the administrations of George H.W. Bush (START I) and George W. Bush (ICOC, SORT), which were perceived as favorable to the United States (P*~T → ~B).The perception of the treaty as fair also serves as a sufficient condition in the second solution term (I*~T → ~B). Here, agreements such as the Outer Space Treaty or the SALT I accords were concluded despite international tensions. The third solution path to a booster role accounts for the Agreed Framework with North Korea in 1994. The weakness of conservative treaty skeptics seems to have contributed to a booster position despite the criticism against North Korea’s trustworthiness (~C*T → ~B). Fourth, the combination of strong conservative treaty skeptics and the perception of a reciprocal treaty is sufficient for a booster outcome. While this seems counterintuitive at first glance, it fits the empirical observation. Obama faced fierce opposition against the New START Treaty from conservative Republicans in 2010 and could barely secure the ratification of a traditional ‘tit for tat’ arms control treaty. Bush easily concluded SORT and ICOC, which were less comprehensive than other compacts. Thus, he faced no opposition from his own party (ICOC was a non-binding agreement concluded without ratification). Overall, the solution term is highly consistent and covers 14 out of 17 cases.

Table 3: Parsimonious solution
Note: Cov = Coverage of solution; uniquely explained cases in bold print. Intermediate solution = P*C*T+I*C*T → B, Con 0.9, PRI 0.9, Cov 0.5; I*~T+~P*C*~T+P*~C*~T+~P*~I*~C*T → B, Con 0.9, PRI 0.9, Cov 0.7. Complex solution = outcome identical to intermediate solution, non-outcome: identical to parsimonious solution.


President Donald Trump signs an Executive Order entitled “Reimposing Certain Sanctions with Respect to Iran” on August 6, 2018 (Official White House Photo by Shealah Craighead)

4. Conclusion

The analysis of US treaty politics revealed a complex pattern. Both Republican and Democratic presidents boosted international arms control since the Cold War. However, only Republican presidents withdrew from existing agreements and several Democratic presidents faced fierce opposition by conservative treaty skeptics in the US Senate. At the same time, the perceived treaty ‘tit for tat’ and the international environment are important conditions that shape US treaty behavior. This fsQCA presented a first step into the research of why the US sometimes pushes for international cooperation and at other times breaks its commitments. It is clear that the current administration and most of its congressional allies perceive international relations as a zero-sum game and disregard the possibility of trustful commitments. Thus, with President Trump and the Republican majority in the Senate, the prospects for a booster role in the field of arms control are more than dim.



Böller, F. and M. Müller 2018. “Unleashing the Watchdogs: Explaining Congressional Assertiveness in the Politics of US Military Interventions.”European Political Science Review 10(4): 637-662.

Dușa, A., 2019. QCA with R. A Comprehensive Resource (Cham).

Krutz, G.S. and J.S. Peake 2009. Treaty Politics and the Rise of Executive Agreements: International Commitments in a System of Shared Powers (Ann Arbor).

Lewis, J.B. et al. 2019. Voteview: Congressional Roll-Call Votes Database (

Mello, P.A. 2014. Democratic Participation in Armed Conflict: Military Involvement in Kosovo, Afghanistan, and Iraq (New York).

Siewert, M.B. 2017.“Qualitative Comparative Analysis.”In Neue Trends in den Sozialwissenschaften: Innovative Techniken für qualitative und quantitative Forschung, ed. S. Jäckle, pp. 273-305 (Wiesbaden).

SIPRI 2018. SIPRI Military Expenditure Database (

Image 1: “In this effort, we stand in total solidarity with the Iranian regime’s longest-suffering victims: its own people.” (Official White House Photo by D. Myles Cullen).

Image 2: President Donald J. Trump signs an Executive Order in Bedminster, New Jersey, entitled “Reimposing Certain Sanctions with Respect to Iran.” (Official White House Photo by Shealah Craighead).


About the Author

Florian Böller works as a post-doctoral researcher at the Heidelberg Center for American Studies and is part of the DFG-funded Graduate Program on Authority and Trust. Among his research focuses are US foreign policy, transatlantic relations, and trust in international politics.

Get in touch on Twitter: Florian Böller

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