Litigation challenging the Affordable Care Act (ACA) finally reached the Supreme Court, where it was granted an unprecedented three days of oral argument. The cases raise fundamental questions about the meaning of Congress’s commerce and taxing powers, questions that reflect underlying debates about how the Constitution’s enduring principles should be interpreted to meet the needs of our complex, modern society. Arguments put forward by the law’s challengers reflect a vision of the Constitution that would cabin federal power and, their opponents contend, roll back decades, if not centuries, of settled law. Is the mechanism adopted for ensuring coverage by the ACA unprecedented or unexceptional? Is a ruling upholding the ACA consistent with traditional notions of congressional power? This debate addressed these and other questions through the lens of the health care lawsuits and offered reflections on the oral arguments in the ACA cases before the Supreme Court.