The Guarantee Clause of the Constitution promises that “[t]he United States shall guarantee to every State in this Union a Republican form of Government . . . .” The Supreme Court has long held this Clause to be nonjusticiable, and as a result, many see the Clause as purely vestigial. But nonjusticiable does not mean toothless, and this view fails to recognize the Clause’s grant of power to Congress. The Guarantee Clause provides Congress with the authority to ensure that each state’s internal governance meets a minimum standard of republicanism. The Framers included this promise because they feared that some forms of government, such as monarchy, were incompatible with republicanism, which they understood as representative self-government. Nonrepublican government in one state, they believed, might have deleterious or even dangerous effects on other states, and protection against nonrepublican government was thus essential for long-lasting and healthy interstate and federal–state relationships. Today, the Framers’ fears appear prescient as a number of states engage in tactics like extreme partisan gerrymandering , which entrenches one party in power; lame-duck legislation, which reallocates power to undermine an incoming administration; and targeted burdens on voting. These tactics parallel the types of democratic erosion that scholars have observed internationally and historically. Moreover, the potential negative effects of these antidemocratic tactics from one state to another, and from one state to the nation as a whole, are substantial and threaten to undermine many of the benefits of federalism. Fortunately, the Guarantee Clause allows — indeed, requires—Congress to address these antidemocratic state-level practices.