When Russia invaded Ukraine on Feb. 24, 2022, the response of the United States and its European allies was to impose economic sanctions on Russia and arm Ukraine for a prolonged war of resistance against Russian occupation. When Ukraine’s defenses proved much more robust than expected, pushing Russia’s army back and retaking territory, the U.S.-led coalition supporting Kyiv poured in advanced weapons and entertained hopes of outright victory. However, a Ukrainian counteroffensive fizzled last year; Russia has proven resilient, economically and militarily. Now, President Vladimir Putin is preparing for a long war, while Ukraine is struggling to rebound from a debilitating six-month pause in U.S. arms deliveries. The United States, and its allies, need to engage in their own fresh thinking about how best to help Ukraine fight back.