Understanding Russia’s Calculus on Opportunistic Aggression in Europe

A shortage of U.S. ISR capabilities in Europe would, for example, degrade NATO’s situational awareness of Russian activity and early warning, leaving the alliance more vulnerable to missing Russian hybrid attacks.

Beyond hybrid actions, U.S. involvement in the Indo-Pacific would also heighten the risk of a kinetic Russian action against a NATO member state. Moscow could come to judge that the absence of key U.S. capabilities would slow a NATO response, giving Russia time enough to seize territory and then use coercion to compel NATO to accept the result. A shortage of key capabilities like long-range precision fires that can hold high-value targets inside Russia at risk and a reduction in NATO maritime power would erode deterrence, with limited air and missile defense leaving allied forces and nations within striking distance of Russia particularly vulnerable. A shortage of strategic enablers, such as C-17s, or sealift could slow reinforcement.

The good news is that the gaps the United States would leave are identifiable. But it will take time for NATO member states to ramp up the specific capabilities needed to fill those gaps. As European countries are increasing defense spending, it is critical for allies to invest some of their greater spending on the capabilities the United States may have to redeploy if its military is engaged elsewhere. The allies should also discuss other approaches to offset the vulnerabilities that would emerge in the event of a crisis in Asia, for example, by determining what more it should pre-position in Europe to avoid the challenges that would emerge from delays in reinforcement. Washington and its allies must think beyond the current war in Ukraine and start making plans and investments now to prevent Russian opportunistic aggression later.

Introduction

Russia does not currently seek a direct war with NATO, especially given the extent to which its military has been degraded by the war in Ukraine. Nevertheless, Moscow has mobilized its defense industrial base and significantly increased defense spending.² Senior U.S. and European officials now assess that Russia could reconstitute its battle-hardened forces in as little as two to five years.³ The Kremlin is also learning important lessons in Ukraine and plans to increase the size of its military beyond prewar levels.⁴ Since its invasion of Ukraine, the Kremlin has grown ever more dogmatic in its intent to not only subjugate Ukraine but also to revise the security order in Europe, including rolling back NATO’s borders, if not undermining the alliance altogether. The intensification of Russian aims to challenge NATO and the West, along with the renewal of its capacity to do so, means that NATO must continue—and accelerate—its efforts to prepare for and prevent a future conflict with Russia.

One scenario stands out as a particularly plausible pathway to a NATO-Russia conflict: The Kremlin comes to underestimate NATO’s, and most importantly, the United States’ resolve to fight under certain conditions. Among the mounting reasons that could lead the Kremlin to believe the United States and NATO lack the will to fight, America’s involvement in a major crisis in the Indo-Pacific would be among the most likely to shape the Kremlin’s calculus. This is because U.S. forces in Europe, or those designated to reinforce Europe, may instead be committed to the Indo-Pacific theater, which the United States has identified as its priority theater, eroding NATO’s conventional deterrence. In this case, Russian President Vladimir Putin could be tempted to test NATO in an effort to undermine the alliance once and for all, judging that Washington would have neither the political interest nor the resources to rapidly come to Europe’s defense and that absent the U.S. capabilities redeployed to the Indo-Pacific, the European members of NATO would be vulnerable.⁵

Since January 2025, the challenge of deterring Russian opportunistic aggression in Europe has taken on even greater salience, given the possibility that President Donald Trump’s administration could downsize America’s presence in Europe. Statements and actions by the Trump administration have called into question the U.S. commitment to defending Europe, and President Trump has repeatedly stated the United States might not come to the aid of European allies if they were attacked.⁶ In his first term, he attempted to reduce the number of U.S. troops in Germany by almost 10,000.⁷ In April 2025, the Pentagon was reportedly considering removing up to 10,000 U.S. troops from eastern Europe, and has made clear that Washington will deprioritize Europe.⁸ It is plausible, therefore, that the reduction of U.S. support for European security may not come about only as a result of a conflict in the Indo-Pacific, but may also be a deliberate policy choice. In either scenario, the Kremlin may look to take advantage of a Europe it perceives to be more vulnerable with reduced U.S. assets and a questionable security guarantee from Washington.

This report focuses on the first of these challenges: the threat of Russian opportunistic aggression in the event the United States is involved in a crisis in the Indo-Pacific, while recognizing that similar dynamics could emerge because of political decisions in Washington. The goal of the report is to articulate the effects of U.S. involvement in a crisis in the Indo-Pacific on European security, including identifying the defense gaps and vulnerabilities that could emerge in Europe and how Russia might seek to exploit these perceived vulnerabilities to advance its aims. To these ends, the paper first briefly outlines the dynamics surrounding a plausible scenario for Chinese aggression in the Indo-Pacific—a Chinese blockade of Taiwan—and identifies in broad terms the U.S. military requirements that would arise because of China’s aggression. Next, the report assesses the gaps this would create in European defense and the resulting impact on NATO’s ability to deter and defend against Russia. Finally, the paper posits how Russia could seek to exploit any such perceived gaps to advance its geopolitical aims. To inform the analysis, the authors conducted an in-depth literature review on the challenges for the United States of facing two simultaneous conflicts with adversaries that are increasingly cooperating, along with holding in-depth interviews and two expert elicitation workshops with former senior U.S. military officials, U.S. defense experts, and experts on Russian political and military thinking.

A conflict in the Indo-Pacific is not inevitable. But it is plausible enough that the United States and Europe must prepare, not least because it could create conditions that significantly increase the risk of direct Russian action against a NATO member state. The good news is that the gaps the United States would leave are foreseeable. However, it will take time for NATO member states to ramp up the capabilities needed to fill those gaps. As European countries are increasing defense spending, it is critical for allies to invest some of this spending on the capabilities the United States wouldn’t be able to provide if its military were engaged elsewhere. NATO may very well remain a superior force capable of defeating Russia in a war, but given the very high costs of war, the goal for the United States and Europe is to maintain a credible enough deterrent that Moscow never tries.