This week, an American president steps onto the world's most consequential diplomatic stages — the United Nations General Assembly and a bilateral meeting with China's Xi Jinping — carrying the full weight of national power but without the allied chorus that has long amplified that power into something greater than itself. The distance between Washington and its traditional partners did not open overnight; it widened through years of transactional choices that treated alliances as costs rather than assets. What unfolds in New York will offer a rare and clarifying test of an old question: wheth