The alliance’s next test will not be measured in percentages of GDP; it will be judged on its ability to defend its territory, defeat aggression, and sustain military operations against a capable adversary.
For too long, discussions about NATO’s effectiveness have been dominated by spending. The argument has been politically useful, particularly in persuading European capitals to invest more, but it has obscured a more important question: what can NATO’s forces actually accomplish?
It’s an important distinction. Spending is an input. Military capability is an output. Operational readiness determines whether it can be employed when needed.
At the 2025 Hague Summit, NATO allies committed to investing 5% of GDP into defense and security by 2035. The commitment marked a substantial advance from the previous 2% benchmark, and by the July 2026 Ankara Summit, European members and Canada had increased defense investment by more than $139bn.
Europe has underinvested in its defense for decades, so the commitments in the face of a deteriorating security environment matter, but NATO cannot afford to confuse financial progress with military effectiveness.
Treating spending as the principal measure of allied performance risks rewarding commitments rather than results.
One country exceeding its spending target does not compensate for a shortage of air defenses, ammunition, intelligence capabilities, or logistics elsewhere in the alliance. Nor does purchasing an advanced weapons system necessarily produce a formation capable of employing it effectively in combat.
NATO already has the framework for a more disciplined approach.
The regional defense plans agreed at the 2023 Vilnius Summit are among the alliance’s most consequential military adaptations since the Cold War. They establish what’s needed to defend allied territory and link operational planning to force structure, readiness, reinforcement, and command arrangements.
The 2025 NATO capability targets build on those plans, identifying the forces and supporting capabilities that need to be developed. These include integrated air and missile defense, long-range weapons, logistics, and large maneuver formations.
This is the correct sequence: Defense plans establish military requirements, capability targets translate those requirements into national responsibilities, and defense investments then produce forces able to fulfill them.
The plans should govern NATO’s decisions about resources, readiness, and the distribution of responsibilities. They should also provide the basis for assessing if the alliance is becoming more capable.
But plans are not proof of readiness.
That requires forces that are available, trained, equipped, integrated, and capable of operating together under demanding conditions. It requires intelligence that supports timely decisions, resilient command and control, ammunition stocks, maintenance capacity, transportation networks, and the industrial ability to sustain operations in a conflict.
Readiness also requires credible assessment through exercises, operational evaluation, and the identification of deficiencies — some of which governments may find politically inconvenient.
An aircraft may be technologically advanced, but its operational contribution depends on intelligence, targeting, aerial refueling, secure communications, maintenance, and available weapons. In the same way, an armored formation may be well equipped, but its effectiveness depends on logistics, air defense, reinforcement, and the ability to sustain losses.
These dependencies are particularly important because of Europe’s reliance on the US. American intelligence, command and control, strategic mobility, long-range strike, and other enabling capabilities remain essential to NATO’s operational effectiveness.
European allies are making progress in addressing deficiencies through greater investment, expanded defense production, and multinational capability development, all of which should improve the alliance’s military position.
But announced programs are not fielded capabilities, and fielded capabilities are not necessarily ready for sustained operations.
The test is whether NATO can execute its regional defense plans with the forces and resources available, not those expected to be available several years from now.
That distinction becomes increasingly important as the US and Europe reconsider their respective responsibilities.
The Trump administration’s NATO 3.0 concept envisages Europe taking primary responsibility for the continent’s conventional defense, while the US retains a strategic role.
The underlying demand is legitimate, and Europe’s economic and industrial capacity should support a much greater contribution to its own defense. The US must also balance its European commitments against responsibilities elsewhere.
The Pentagon’s review of American military posture in Europe could produce significant changes in troop deployments, basing, command responsibilities, and the capabilities available to NATO commanders.
The danger is not that US conventional forces will be reduced; it is that reductions could occur before European replacements are ready.
A decision to withdraw American capability may be politically straightforward, but replacing its operational contribution could require years of procurement, training, integration, and exercises. Russia will make its own calculations about opportunities and vulnerabilities.
Washington’s political timetable, Europe’s ability to generate military capability, and Russia’s evolving threat are unlikely to align.
NATO therefore needs an explicit standard for managing the transition. Changes in US contributions must be assessed against the requirements of regional defense plans and the demonstrated readiness of European forces.
The US midterm elections have added another dimension.
As a recent analysis by the International Centre for Defence and Security observed, the 2026 mid-term elections have changed Washington’s political balance without resolving Europe’s underlying strategic challenge.
While the incoming Democratic majorities suggest renewed congressional oversight and cooperation on European security, a change in Congress is not a change in the presidency. Congress can influence American policy through legislation, appropriations, and oversight, but the executive retains substantial authority over military posture and foreign affairs.
And Congress has already demonstrated its concern about US force reductions. The Fiscal Year 2026 National Defense Authorization Act imposes conditions on the use of funds for reductions in American military personnel, equipment, facilities, and command responsibilities in Europe. The legislation requires independent assessments of their consequences for American and NATO security interests.
These provisions matter, but effective congressional oversight also depends on an accurate understanding of the operational risks involved.
European governments face a difficult political calculation. Many have sought to avoid direct confrontation with Washington over NATO 3.0 while emphasizing their commitment to increased defense investment and greater responsibility.
There are understandable reasons for that approach, and preserving influence with the administration and shaping decisions through consultation may accomplish more than public disagreement. Yet diplomatic restraint has limits.
If Europeans publicly embrace a redistribution of responsibilities without clearly identifying the military requirements for its success, they risk weakening the position of their supporters in Congress. Legislators may find it harder to contest changes in American force posture when the allies most directly affected appear willing to accept them.
This does not require European leaders to oppose NATO 3.0 or defend the existing distribution of responsibilities indefinitely, but it does need them to distinguish between support for the objective and acceptance of every measure proposed to achieve it.
European governments should be explicit about which missions they can assume, which critical capabilities remain dependent on the US, and what must happen before American contributions can be reduced.
Congress should demand comparable rigor from the administration.
Any significant change in American contributions should be assessed against demonstrated European readiness, the continued availability of critical enabling capabilities, and the alliance’s ability to execute its assigned missions throughout the transition.
Where operational risks remain, they should be identified, mitigated, and explicitly accepted through appropriate allied decision-making and congressional oversight.
Europe must become substantially more capable, and a more balanced alliance could be stronger and more durable, but transferring responsibility does not automatically transfer capability.
NATO has the defense plans, and its members have made the spending commitments. The remaining task is to ensure the forces, capabilities, and readiness required are available, and remain available as American and European responsibilities evolve.
NATO’s most dangerous gap is between what its leaders have agreed the alliance must do and what its forces can deliver. Closing it must come before declaring the transition a success.
David M. Cattler is a Senior Fellow at the Center for European Policy Analysis (CEPA). He is a senior transatlantic security leader with more than 35 years of experience across the US government, NATO, and the Intelligence Community. Most recently, he served as Director of the Defense Counterintelligence and Security Agency (DCSA) and was previously NATO’s Assistant Secretary General for Intelligence and Security, the alliance’s senior intelligence official. Cattler is a graduate of the US Naval Academy and Georgetown University and was an MIT Seminar XXI Fellow.
Europe’s Edge is CEPA’s online journal covering critical topics on the foreign policy docket across Europe and North America. All opinions expressed on Europe’s Edge are those of the author alone and may not represent those of the institutions they represent or the Center for European Policy Analysis. CEPA maintains a strict intellectual independence policy across all its projects and publications.
