American political commentators have frequently called for the U.S. president to take effective action to improve world economic growth. Such calls are a form of what Matthew Yglesias has dubbed “Green Lanternism”—the unspoken theory that the U.S. president’s ability to affect outcomes is primarily affected by his willpower. In this article, I examine the opposite—and more plausible causal relationship—that the power of the U.S. president is shaped by the underlying secular determinant of world economic growth. I go on to examine how we might expect U.S. power and interests in building up a multilateral trading order could largely wither away under conditions of enduring weak economic growth, which some economists have argued is in fact the most plausible long-run growth path for the world economy.