U.S. primacy is both a strategic choice and an empirical condition, and thus analysis regarding the future of U.S. primacy should focus on both ideational (i.e., policy choices) and material variables (i.e., relativities of power).1 We are now witnessing significant shifts in the realms of U.S. primacy that carry great weight for Australia. In material terms, while the United States remains dominant across a range of measures (e.g., military spending),2 it has faced with growing intensity the great challenge of all hegemonic powers-managing never-ceasing political and military commitments and maintaining the economic capability to meet them.2 The Obama administration has attempted to grapple with this central challenge via the retrenchment of military commitments in Iraq and Afghanistan, budget sequestration, and a concerted effort to avoid new military and security commitments.4The results of this strategic choice to retrench U.S. commitments to a more manageable level, however, have been problematic at both the ideational and systemic levels. Ideationally, as amply demonstrated by the 2016 presidential election, we have seen the rise of a restraint constituency among a significant segment of the U.S. public that openly questions both the viability and desirability of maintaining U.S. primacy in international affairs.5 In a systemic context, perceptions of U.S. retrenchment have also stimulated both adversaries and allies alike to consider the limits of U.S. primacy. As Robert Jervis has noted, primacy not only means being much more powerful than any other state according to the usual and crude measures of power (e.g., gross national product, size of the armed forces, and lack of economic, political, and geographic vulnerabilities) but also, by virtue of this standing, means having the ability to establish, or at least strongly influence, 'the rules of the game' by which international politics is played, the intellectual framework employed...and the standards by which behavior is judged to be legitimate.6The subsequent discussion focuses on the impact of current challenges to the current U.S.-led international order derived from both the systemic and ideational levels for the future of the U.S.-Australia alliance. It argues that while Australia, like other U.S. allies in Asia, has been sensitive to the challenges to U.S. primacy posed by states such as Russia and China and has adjusted its defense and strategic policy accordingly, it has not adequately considered how such systemic pressures have negatively affected American perceptions of the durability of U.S. primacy.Australia and Challenges to U.S. Primacy under ObamaAn international order, as Henry Kissinger famously put it, is legitimate if all great powers accept their role and identity within it and embrace certain baseline conventions and rules governing interstate behavior.7 Adversaries such as Russia and China-through their actions in Ukraine and the South China Sea-have clearly used the Obama administration's attempts at retrenchment as an opportunity to challenge the baseline conventions and rules of the current international order and in doing so test the limits of U.S. primacy. Some U.S. allies, such as Japan, South Korea, and the Philippines, have also begun to consider with much greater alacrity their strategic options-from greater defense self-reliance to potential bandwagoning with a rising China-should such trends continue.These trends should also be highly concerning for policymakers in Canberra. While there has been significant academic debate in Australia regarding the significance and impact of the rise of China on the country's national security and the U.S.-Australia alliance, official policy for the past several years has attempted to hedge between the realities of deep economic engagement with Beijing and underlying concerns regarding its strategic intentions throughout Asia.8 The latter concern has resulted in efforts to strengthen the alliance with the United States on the basis that strengthening the alliance network and joint capabilities will complicate the strategic picture for China in various theatres and dissuade Beijing from even more assertive and possibly reckless policies in the region. …