Two key factors in the international system might affect changes in presidential doctrines. One factor is the distribution of capabilities: is the system unipolar or bipolar/multipolar? Under unipolarity, a great power might try to promote its own ideology—international liberalism in the case of the US. However, when there are a number of great powers, realist doctrines will be very appealing. The other key causal factor is the level of threat confronting the great power. As the level of threat confronting the US is rising, the doctrine will become more offensive, aiming to maximize its relative power and to weaken its rivals. In the post-Cold War era under unipolarity, the US got the chance to carry out a liberal doctrine. Under Trump, the doctrine shifted to a nationalist-America First strategy with some realist elements—the US aimed to maximize short-term material gains unilaterally—transactional deals in which the US should be always the winner and the other side would be the loser. The explanation is power transition toward multipolarity and the rising level of threat in the international system—as both China (notably, in the South China Sea) and Russia (with the 2014 annexation of Crimea) became more aggressive. Before he became president, Joe Biden shared the international liberal agenda of various post-Cold War administrations. This agenda included the attempts to integrate China and Russia into the liberal international order, notably including China in the WTO and Russia in the G8. However, by the time he moved into the White House, the international system changed in some major ways, most notably with the rise of a peer great-power competitor—China. This shift compelled Biden to endorse a realist doctrine, focusing on great-power competition. In the first year of his administration, Biden led a defensive realist doctrine-competition with China but in a restrained and cautious manner with a focus on deterrence and balancing. This defensive doctrine included also withdrawal from Afghanistan in summer 2021 and a major attempt to revive the nuclear deal with Iran. The Russian invasion of Ukraine and the rising level of threat led, however, to a shift in the doctrine toward a more offensive orientation. The offensive realist doctrine, aiming at weakening Russia, was reinforced by the heroic resistance of the Ukrainians to the Russian invasion. The administration is willing to provide a major package of military aid as part of a realist agenda which encourages such aid when the client demonstrates its willingness to defend itself under the realist logic of a self-help international system and the client shows the capacity to cause major damage to a threatening rival of the US. Finally, the overall realist doctrine might be qualified later on by some liberal elements of dealing with global/transnational threats which were upgraded in recent years: pandemic; climate change and nuclear proliferation. These threats demand international cooperation, most notably with China. Still, under great-power competition and rising levels of threat, we might expect that the realist elements of the doctrine will be the most salient.
