There is a peculiar ritual in transatlantic relations: every few years, European leaders gather to announce, with great solemnity, that they are finally committed to spending 2 percent of GDP on defense. Applause follows. The Americans smile. Nothing much changes.

The 2 percent target, adopted at the 2014 Wales Summit in the aftermath of Russia's first invasion of Ukraine, was a political compromise, not a strategic calculation. It was the minimum number that NATO's European members could plausibly commit to without causing domestic political crises. It bore no relationship to the actual cost of defending Europe.

The Math Does Not Work

Consider what 2 percent buys. For a country like Germany (GDP of roughly €4.1 trillion), 2 percent means approximately €82 billion in annual defense spending. That sounds like a lot. It is not.

Germany must simultaneously recapitalize its army, which has been systematically underfunded for three decades; contribute to NATO's enhanced forward presence on the eastern flank; invest in next-generation air and missile defense; modernize its nuclear sharing arrangements; and maintain an expeditionary capability for out-of-area operations.

Military planners in Berlin privately acknowledge that the real requirement is closer to €140 billion per year, roughly 3.4 percent of GDP. The gap between what the politics allow and what the strategy requires is where European security risk lives.

What America Should Say

American policymakers have been too polite about this for too long. The diplomatic fiction that 2 percent represents a meaningful commitment has allowed European allies to claim progress while remaining strategically dependent on the United States.

The honest conversation, the one that needs to happen, is this: Europe faces a conventional military threat from Russia that it cannot counter without either spending dramatically more on defense or remaining permanently dependent on American power projection. There is no third option.

Dependency is not inherently shameful. It is, however, a strategic choice with consequences. A Europe that depends on American military power has less leverage to disagree with American policy on other matters: trade, technology regulation, China. European leaders who want strategic autonomy must be willing to pay for it. So far, they have not been.

The Coming Reckoning

The political sustainability of America's European security commitment is not unlimited. Public opinion surveys consistently show that Americans support NATO in the abstract but are less enthusiastic about bearing a disproportionate share of the cost. This sentiment cuts across party lines.

A serious European defense effort, one that would allow the continent to credibly deter Russian aggression without American reinforcement, would require sustained spending in the range of 3 to 4 percent of GDP for a decade or more. This is not a controversial estimate among defense economists. It is simply one that no European politician wants to say out loud.

They should start.