President Trump has issued a stark warning to America’s allies: those who refuse to help secure the Strait of Hormuz will be remembered. In an interview with the Financial Times, Trump argued that the countries benefiting most from oil flowing through the strait — particularly Europe and China — should contribute to protecting it. If they do not, he says, the consequences for NATO could be serious.

Several European leaders appear reluctant. Norway’s Prime Minister Jonas Gahr Støre has said the Gulf crisis is “not our table,” and European officials increasingly describe the confrontation with Iran as America’s war, not theirs.

For Trump, this is not only about Iran. It is about reciprocity inside the Western alliance. The United States helped Europe in Ukraine, he argues — now Washington expects the same solidarity in return. The question now facing NATO is blunt: Can an alliance survive if members decide case by case which conflicts they are willing to support?