As the story goes, when Benjamin Franklin left the Constitutional Convention in 1787, he was approached by a woman who wanted to know what type of government the delegates created. Franklin responded, "A republic, madam, if you can keep it." Since the Founding, the Supreme Court has never directly defined what this "Republican Form of Government" is that Article IV of the Constitution guarantees to every state in the union — but cases come up every now and then invoking this provision (also known as the Guarantee Clause). The latest such case comes out of Colorado and involves the ability of voters, protected in nearly every state constitution, to make law through various forms of direct democracy, such as voter initiatives. In 1992, Centennial State voters enacted a Taxpayers Bill of Rights (TABOR) to restrict the legislature's ability to raise tax rates or increase spending, in a formula tied to the rate of inflation and population growth, unless otherwise approved by voters. In Kerr v. Hickenlooper, the plaintiffs wish to remove this barrier and provide the Colorado legislature, municipalities, and school boards with full discretionary authority to tax, spend, and borrow, without voter approval. State Senator Andy Kerr and other government officials are seeking to redefine a "republic" as an institution whereby all legislation is solely the duty and privilege of the legislatures, and voter referenda are impermissible. The outcome of this revised interpretation could invalidate centuries of voter decisions at the ballots, abolish future voter input aside from the election of representatives, and give politicians carte blanche to tax, spend, and borrow. Surprisingly, and despite any showing that voter initiatives are somehow incompatible with "republican government," the federal district court allowed the lawsuit to proceed. Now before the U.S. Court of Appeals for the Tenth Circuit, Cato has joined the Independence Institute on an amicus brief arguing that, absent controlling legal precedent, the phrase "Republican Form of Government" should be defined by the standard sources the Supreme Court uses to decipher constitutional language: Eighteenth century political works, contemporaneous dictionaries, and official records and commentary from the Constitutional Convention, which for our purposes here all define "republic" in a way fully consistent with direct citizen lawmaking. The most popular example of voter participation at the time of the Founding was through the town meeting, employed to this day throughout much of New England. Moreover, Massachusetts ratified its state constitution of 1780 by referendum, and Rhode Island even used a referendum to ratify the U.S. Constitution itself. Entry of those states into the union entailed recognition that those existing states had a republican form of government. Based on all available evidence, the Guarantee Clause doesn't require Colorado to dismantle its TABOR system of checks and balances. We urge the Tenth Circuit to reverse the district court's denial of Colorado's motion to dismiss and allow the state to preserve its model of self-governance.