Trump has changed the game completely. In line with Schelling’s expectations, his perceived unpredictability is adding credibility to the threat that he might actually withdraw U.S. forces even if it is not in the United States best interest to do so. There is genuine concern among U.S. allies about what Trump might do if they do not take immediate steps to increase their defense spending. Many have already taken steps in this direction, or signaled their intention to do so. In December 2016, Japan adopted a record high defense budget, which allocated considerable funds to the procurement of American equipment, notably F-35s and missiles. The South Korean government reacted to Trump’s election by vowing to increase defense spending significantly if he insists on it. Likewise, the Danish Prime Minister Lars Loekke Rasmussen promised to increase defense spending after his first phone conversation with Trump. In Germany Trump’s election triggered a hitherto unthinkable debate on whether Germany should develop nuclear weapons.

Trump cannot take sole credit for the newfound allied attentiveness to longstanding U.S. demands. The Japanese defense budget has been increasing in recent years due to growing concerns about China. Russia has had a similar effect on the defense budgets of the eastern NATO members. However, Trump has made a crucial difference by completely changing the debate on defense spending in allied capitals, significantly strengthening the hands of the proponents of increased defense spending in allied governments. The 2016 IHS Jane’s Defence Budgets Report consequently expects European NATO allies and partners such as Finland and Sweden to boost their defense spending by about $10 billion over the next five years.

That Schelling’s logic applies equally well to President Trump’s dealings with America’s opponents has already been pointed out by other commentators. They have referred to Nixon’s madman theory of negotiation, which holds that America’s opponents will tread more carefully if they perceive the president to be unpredictable or crazy. It has been debated at some length whether Trump is using this theory in a rational manner to extract concessions from U.S. adversaries, or if he is “a madman in practice.” Regardless, the point is that President Trump’s unpredictability makes it next to impossible to calculate the risk of escalation involved in challenging the United States militarily, a concept also highlighted by Schelling. President Obama’s reluctance to threaten and use force likely emboldened China and Russia to take greater military risks in Eastern Ukraine, Syria, and in the East and South China Seas. While Beijing and Moscow could be fairly confident that Obama would not take military counter-measures, they have no way of knowing what President Trump might do. It is very easy to imagine him giving the order to down a Chinese or Russian plane to demonstrate that “America is great again.”