This Article reframes the way we think about Justice Frankfurter — not as a Warren Court antihero but as an opponent of judicial supremacy, forerunner of popular constitutionalism, and exemplar for scholars who criticize the Court's Affordable Care Act and other recent decisions as contemptuous of Congress and other elected branches. Frankfurter shared Jefferson's faith in the democratic political process and enlightened public opinion and distrusted courts as historically reactionary institutions that thwarted the popular will and social change. This is the first article to broaden the definition of popular constitutionalism beyond political and social movements and elected officials to include the Supreme Court justices themselves. By arguing that Justices can be popular constitutionalists, this Article links judicial restraint with popular constitutionalism. Frankfurter's judicial restraint stemmed from his belief that the democratic political process was a more enduring, effective, and legitimate method of protecting civil liberties and producing constitutional change. His last opinion, his dissent in Baker v. Carr, warned about the evils of judicial supremacy. Bush v. Gore and Citizens United made his Baker dissent seem prophetic. This Article invites scholars to rethink how Frankfurter's jurisprudence fits into the ongoing debate about the role of the Court and into progressive constitutional theories including popular constitutionalism.