Introduction: Out With the Old, In With the New? Explaining Changing EU–US Relations

When Russia invaded Ukraine in February 2022, Europe and the US quickly joined in a strong and coordinated response. But how significant is the Ukraine crisis response for longer‐term trends in transatlantic relations? This thematic issue addresses this question by focusing on the factors that affect the strength of the transatlantic relationship. Only by explor‐ ing the impact of various structural, strategic, economic, institutional, and domestic factors can we better understand the current and future state of EU–US relations—both in normal times and in times of crisis. Two questions are explored across cases: First, is the EU–US relationship changing in various fields? Second, how can the putative changes (or stabil‐ ity) in EU–US relations be explained? For this purpose, the articles also operationalize and apply a common explanatory framework. This Introduction sets out and justifies the overall research questions, develops the analytical framework, and briefly explains the empirical focus of the articles that follow.


Introduction
At the time of writing, relations between the European Union (EU) and the United States (US) seem more robust than ever. When Russia invaded Ukraine in February 2022, Europe and the US quickly joined in a strong and coordinated response, involving all means except direct military confrontation with Russia. The EU member states have again proved able to unite in crisis (Riddervold et al., 2021), and NATO and the EU have been coordinated in their response, so far avoiding the scenario some have feared might follow as the EU grows stronger in the foreign and security policy domain. It seems like the transatlantic relationship stood the test when push came to shove. But how significant is the Ukraine crisis response for longer-term trends in transatlantic relations? Does the coordinated response suggest that the transatlantic relationship is back to normal? In other words, has it returned to the strong relationship we saw before Obama's pivot to Asia and Trump's questioning of the relationship? Or are we nonetheless witnessing changes in the transatlantic relationship that go beyond immediate crisis responses and any sitting US president? This thematic issue addresses these questions by focusing on the factors that affect the strength of the transatlantic relationship. Only by exploring the impact of various structural, strategic, economic, and domestic factors can we better understand the current and future state of this traditionally strong and globally important relationship-both in normal times and in times of crisis. Transatlantic relations, defined as "the overall set of relations between the European Union and the United States, within the broader framework of the institutional and other connections maintained via NATO and other institutions" (Smith, 2018, p. 539), have been a key feature of international relations since the end of World War II. US-Europe relations form the very core of, and largely determine, the structure and content of the post-war "International Liberal Order" (Alcaro et al., 2016;Hill et al., 2017;Ikenberry, 2018). However, over the last decade, scholars and observers have questioned the strength of this relationship, under US President Trump in particular. Indeed, President Trump signaling that "the very basis of the relationship with Europe no longer fits with U.S. values, needs, and interests" (Anderson, 2018, p. 27) led scholars to suggest that EU-US relations might be weakening (Riddervold & Newsome, 2018a;Rose, 2018;Smith, 2018;Walt, 2017). In a 2018 issue of Foreign Affairs (Rose, 2018) with the telling title "Letting go. Trump, America and World Order," a number of scholars discussed the present and future of the US leadership role in the international liberal order, including US relations with Europe. They concluded that the transatlantic relationship indeed seemed to be weakening, also beyond Trump, since the US is becoming less concerned with upholding its traditional bonds to its Atlantic partner (Rose, 2018). In the most comprehensive and systematic study of the impact of multiple EU crises and a changing US foreign policy on the transatlantic relationship, a special issue in the Journal of European Integration (Riddervold & Newsome, 2018b) also concluded that although the long term effects remain to be seen, "the transatlantic relationship is under more pressure today than in any other period since its establishment after the Second World War, putting the strength of the transatlantic, institutional structure to a particularly hard test" (Riddervold & Newsome, 2018a, p. 518).
Scholars suggest that the transatlantic relationship is not likely to go back to the pre-Trump era, arguing that there are long-term challenges facing EU-US relations even if it proved strong in the immediate response to Russian aggression in Ukraine (Schwartz, 2022;Smith, 2022;Walt, 2017). Structurally, the US' long-term challenger is still China, not Russia. Also, domestic policies are vital to understanding US foreign policy. Trumpism has not disappeared from US domestic politics and may return with a new administration. One can only speculate what the (transatlantic) response to the Russian invasion would have looked like under a more Trumpist US administration. The relationship has however survived crises like that caused by Trump before and might do so this time as well (Anderson et al., 2008)-perhaps in particular if the EU and the US find their way back to a longerterm common response to Chinese and Russian policies.
Against this background, this thematic issue sets out to systematically describe and explain a putatively changing EU-US relationship. First, the claim that the transat-lantic relationship is weakening beyond the effects of any one sitting president needs further substantiation before more general conclusions can be drawn. Second, if the relationship indeed is changing and even becoming weaker in the longer term, its causes remain to be studied systematically from a theoretical perspective. In spite of much public and scholarly debate about whether or not the transatlantic relationship is changing, there are no studies that comparatively explore not only if but also why transatlantic relations potentially are changing (or not). Knowing how entangled the two Atlantic partners have become over the last 70 years, this gap in the literature is puzzling and is what this thematic issue will address.
The remainder of this Introduction draws on international relations (IR) and EU integration theory to develop a common analytical framework, discussing the many various and often interacting factors that potentially influence the strength of the EU-US relationship. It then briefly presents the various cases explored in the articles that follow. The findings are summarized in the thematic issue's Conclusion (Newsome & Riddervold, 2022).

Studying EU-US Relations: Analytical Framework
The transatlantic relationship is a complex and multifaceted relationship that is affected by several different and often interacting factors ranging from economic and strategic interests, ideas, and institutional factors to the broader global structures in which they take place. In the words of Mike Smith in this issue, the transatlantic relationship is "a structured array of markets, hierarchies, networks, ideas, and institutions" (Smith, 2022, p. 219) that affects and is affected by the broader international structure and world order in which it operates. Studying any of these factors in isolation will thus give an insufficient picture of the relationship, even within a particular field or policy domain. After all, no other regions of the world are today as closely connected in economics, security, institutions, values, and politics as Europe and the US (Oliver, 2016, p. 2; see also Alcaro et al., 2016;Hill et al., 2017). Nonetheless, to systematically tease out the various factors that affect the transatlantic relationship, we draw on different theoretical perspectives and previous studies to develop a common framework distinguishing between five factors that putatively contribute to explaining a weakening or stable/strengthening relationship in our cases. Although analytically distinct, we treat them as empirically overlapping and potentially complementary. Hence, they may vary across cases and over time and may complement each other in any one case. While three of these perspectives are in line with the conventional explanations of the transatlantic relationship, focusing on interests, security, and institutions, we draw on cleavage theory and a constructivist crisis perspective to develop two alternative explanations that are seldom linked to studies of transatlantic relations: the importance of actors' trust in and perceptions of the relationship as such, and the role of domestic support. All the articles in the thematic issue relate to some or all of these factors and also discuss other aspects of the relationship, where relevant.
According to neo-realist/realist perspectives, relative power structures determine EU-US relations (Mearsheimer, 2014;Waltz, 1979). With changing geopolitical structures, the EU-US relationship may thus also change. On the one hand, the EU and the US may strengthen their relationship to balance other emerging powers that threaten the status quo or threaten their security. At the outset, the Russian invasion of Ukraine would suggest such dynamics, which could also be an expression of more long-term trends. Scholars have already suggested that the ongoing conflict with Russia may lead to a new cold war between the West on the one hand and Russia and China on the other, mainly depending on the extent to which China decides to support Russia (Beckley & Brands, 2022). The two might also want to cooperate vis-à-vis China to uphold US' hegemony more broadly, or agree on a division of labor where the US supports Europe on Russia, and the EU is loyal to the US in its dealing with China (Cross & Karolewski, 2017). On the other hand, the growth of China and the relative decline of Europe may, after the immediate Ukraine crisis is over, once again lead to the US focusing on Asia rather than Europe, and over time lead to a weaker transatlantic relationship (Schwartz, 2022;Smith, 2022). The EU might also want to increase its own global power and independence vis-à-vis the US, or in light of changing US foreign policies under various administrations, consider its strategic interests better served by seeking other alliances.
A liberal intergovernmentalist perspective would also look at the transatlantic relationship as a transactional relationship primarily determined by broader structural changes. However, rather than explaining its strength based on geopolitical trends and strategic interests, a liberal intergovernmentalist approach explains transatlantic relations on the basis of the actors' economic interests and interdependencies (Ikenberry, 2018;Keohane & Nye, 2012;Krasner, 1999). Ikenberry (2018) thus expects the transatlantic relationship and the liberal order overall to remain strong also in the future owing to a shared economic interest in the maintenance of that order: The high level of globalization, interdependence, and a common interest in open, well-functioning markets create a push for cooperation in search of efficient solutions to common challenges. According to Keohane and Nye (2012), interdependencies are active relationships that are costly to break. If there are high costs associated with a weakening relationship or strong economic benefits of a strong cooperation, one would thus expect the relationship to remain strong, even in the face of changing geopolitical contexts. On the other hand, if they do not perceive a strong relationship as valuable, or even believe other relationships to be more valuable in economic terms, one would instead expect a weak relationship to emerge. We have, for example, already seen the EU responding to US protectionism under Trump by seeking economic partnerships with other actors such as Japan and China. Moreover, it is increasingly challenging to distinguish economic factors from strategic issues. Not least in the technological realm, where the US, for example, has presented Chinese 5G providers as a security threat and asked its allies to refrain from using them. The EU and the US also disagree on several issues, such as how to tax and regulate (often American) tech companies.
An alternative set of factors start from the understanding that other factors such as norms and institutions may influence foreign policy behavior and thus the strength of the transatlantic relationship at any one time (Kratochwil, 1989;March & Olsen, 1998;Risse, 2016). If we find evidence to suggest a strong/stable relationship across some or all of our cases, various institutionalist approaches would hypothesize that this is so because of the large number of already existing common institutions. Institutions are "persistent rule structures that prescribe appropriate behaviour, and enable or constrain behaviour" (Risse, 2016, p. 24) and can be formal (such as NATO) or informal (such as established patterns of cooperation within multilateral institutions). Within such institutions, policy-makers act based on existing pathdependent habits and internalized norms of behavior (March & Olsen, 1998); in this case, the practices, expectations, and obligations that have become institutionalized and internalized in the transatlantic community, where cooperation takes place almost automatically.
These roles may also be triggered in times of crisis, where shared perceptions and world views may come to the fore, as we have seen in Ukraine: The EU and NATO have for example been clear not only on the strategic threat posed by Russia but also on the importance of protecting a particular view on international law, where sovereignty and human rights are protected. Such established norms and roles may, however, also be challenged or revoked when faced with crises and challenges. A crisis may entail a fundamental questioning of pre-existing governance arrangements and "long-cherished beliefs" in existing solutions (Lodge & Wegrich, 2012, p. 11), or produce critical junctures that generate "windows of opportunity" for significant policy change (Kingdon, 1984). When established structures and taken for granted scripts are disrupted-which is what happened with the Trump crisis (Anderson, 2018)we might over time thus also observe a weakening of the EU-US relationship. To further our understanding of the relationship, we thus also consider two additional factors linked to perceptions that may be particularly relevant for clarifying a weakening of the relationship: the importance of actors' trust in and perceptions of the relationship as such, and the role of domestic support.
Our fourth factor builds on social constructivist core assumptions and, drawing from Cross (2021), adds to this perspective by suggesting that the transatlantic relationship rests on various actors' perceptions of its strength and viability, and, in particular, on whether or not the relationship is perceived of as being in crisis (or not). Social constructivist perspectives assume that norms and ideas may influence actors' preferences and identities and thus regulate behaviour (Cross, 2022;Kratochwil, 1989;Risse, 2016). Interests and preferences are not given, but socially constructed through various processes of social interaction, such as argumentation, learning, deliberation, norm diffusion and the like, where both state and non-state actors may play important roles (Cross, 2021). Hence, a key issue for understanding the strength of the transatlantic relationship would be linked to how it is perceived, which again would have consequences for various actors' behavior and relations to others. More precisely, to study this possibility empirically, we draw on Mai'a Cross' concept of societal or integrational panic developed to study the social construction of crisis in the EU. Cross argues that "crises must be seen to threaten whatever defines the current order of things….It takes opinion-makers…and various other social actors to construe an event as a crisis in order for it to be recognized as such" (Cross, 2021, p. 195, emphasis in original). In the EU, Cross underscores: Integrational panic occurs when there is some form of overreaction to events, as well as the consolidation of narratives about these events, defining them as crises of EU integration. This disproportional reaction often brings pre-existing societal tensions to the surface that are not necessarily directly related to the crisis event itself, but then lead to the perception that societal or political breakdown of some kind is imminent. (Cross, 2021, p. 199) This type of societal panic may hence also be vital in understanding the strength of EU-US relations: On the one hand, if a crisis is perceived as a common crisis amongst actors on both sides of the Atlantic, it may bring them closer together in common responses and shared role conceptions. If, on the other hand, the relationship itself is portrayed as being in crisis or in decline owing to mutually perceived antagonistic deficiencies of the other partner, this may, over time, have consequences for their trust in the relationship. That would in turn affect their behavior towards each other. As mentioned in the introduction above, Trump's break with traditional US foreign policies was a crisis for Europe (Anderson, 2018), and may lead Europeans to distrust the stability of the American commitment also in the longer term, even if they stand together in the immediate threat to European security caused by the Russian invasion of Ukraine. While both the US and EU leaders have taken the transatlantic relationship more or less as a given, Trump showed that international voluntary institutions over time are only as strong as the actors make them. The EU now knows that US policies may change again and that common institutions can be challenged. European political actors also recognize that the US foreign policy focus, indepen-dent of any sitting president, is less on Europe than earlier. At the same time, continuous cooperation between European and US actors at lower levels may serve to contradict such trends, and instead serve to uphold trust and a strong relationship, more or less independently of what goes on at a higher level (Cross, 2022).
A fifth aspect that might affect the strength of the relationship is linked to domestic support for transatlantic relations and international cooperation more broadly. More precisely, to develop this argument, we draw on Hooghe and Marks' (2018) post functional cleavage theory to understand the support of, and opposition to, European integration amongst the EU population. According to this perspective, populism in Europe is due to a clash between the functional need for more European integration in response to common challenges on the one hand and local identities on the other, over time leading to the development of a new and increasingly salient transnational party cleavage. At its core, this new party divide is linked to a conflict over the role of the nation-state and hence also linked to voters' perceptions and parties' positions on the EU. Studies of increasing US polarization show similar patterns of support and opposition to international cooperation, suggesting that there is a new and increasingly important cleavage between voters who are referred to as the winners and losers of globalization (Peterson, 2018;Zürn, 2018). We also know that domestic issues are crucial to understanding foreign policy behavior, not least in the US (Olsen, 2022). As argued by John Peterson in 2018, "the fate of the liberal international order begins at home" (Peterson, 2018, p. 649)-an insight that is relevant for the EU-US relations as well. Nonetheless, these insights have seldom been applied in studies of transatlantic relations.

Cases Explored in This Thematic Issue
To answer our research questions, the articles in this thematic issue conduct analyses across cases in two thematic areas that form the core of EU-US relations, namely EU-US security relations and EU-US relations in multilateral frameworks. Together they provide a broad picture of the relationship. The first set of articles explores EU-US security relations. Gorm Rye Olsen discusses the development of the relationship across four key cases: NATO, the US pivot to Asia, the sanctions policy towards Russia, and, finally, the Afghanistan debacle (Olsen, 2022). Bjørn Olav Knutsen explores the long-term changes in EU-US relations and how these changes affect the development of EU security and defense policies (Knutsen, 2022). Pernille Rieker explores transatlantic security relations in Africa (Rieker, 2022), while Mai'a Cross discusses transatlantic security relations in space (Cross, 2022). Lastly, in one of their cases, Kolja Raube and Raquel Vega Rubio's cases discuss EU-US relations vis-à-vis China over the AUKUS deal (Raube & Vega Rubio, 2022).
A second key pillar of EU-US relations in the foreign policy domain is their interactions and relations in multilateral institutions. Ingrid Hjertaker and Bent Sofus Tranøy explore EU-US financial relations over time and in times of financial crises (Hjertaker & Tranøy, 2022), Mark Schwartz analyzes EU-US trade relations (Schwartz, 2022), and Bart Kerremans explores EU-US relations in the World Trade Organization (WTO; Kerremans, 2022). In one of their two cases, Kolja Raube and Raquel Vega Rubio discuss EU-US relations vis-à-vis China in response to human rights violations (Raube & Vega Rubio, 2022).
In the final article before the conclusion, Mike Smith discusses the broader patterns of EU-US relations, focusing on its strength and status within a changing geopolitical order, and how various factors together serve to form a changing relationship (Smith, 2022). The concluding article (Newsome & Riddervold, 2022) summarizes the findings and discusses their empirical and analytical implications.