This section is called the Guarantee Clause, because by its terms the federal government makes certain guarantees to the states. One of these— protection from foreign invasion—continued Congress’s prior obligation under the Articles of Confederation. This guarantee is related to the principle that although the federation may be decentralized internally, it is to have a substantially common foreign policy and be seen as a unified sovereign in international law.

The other principal guarantee in Article IV, Section 4 is that the federal government will assure the states “a republican form of government.” This assurance did not appear in the Articles of Confederation. The guarantee of protection from domestic violence can also be seen as part of the republican guarantee.

Founding-era dictionaries defined a “republic” as a “commonwealth,” a “free state,” and “a state or government in which the supreme power is lodged in more than one.” In other words, a republic was a state governed by those citizens who enjoyed the franchise rather than by a monarch or autocrat. Accordingly, founding-era dictionaries often defined “republican” as “placing the government in the people.”

Despite some shades of difference, the views of those participating in the constitutional debates of 1787–1789 were broadly consistent with the dictionary definitions. There was, moreover, a consensus as to three criteria of republicanism, the lack of any of which would render a government un-republican.

The first of these criteria was popular rule, broadly understood. The Founders believed that for government to be republican, political decisions had to be made by a majority (or in some cases, a plurality) of voting citizens. The citizenry might act either directly or through elected representatives. Either way, republican government was government accountable to the citizenry. To a generation immersed in Latin learning and looking to pre-imperial Rome for inspiration, a republic was very much res publica—the people’s affair.

The second required element of republican government was that there be no monarch. The participants in the constitutional debates believed that monarchy, even constitutional monarchy, was inconsistent with republican government. When Alexander Hamilton proposed a president with lifetime tenure, the delegates disagreed so strongly that they did not even take the time to respond.

The third criterion for a republic was the rule of law, a concept deemed fundamental to a free state. The Framers believed that ex post facto laws, bills of attainder, extreme debtor-relief measures—most kinds of retroactive legislation, for example—were inconsistent with the rule of law, and therefore un-republican.

Some participants in the ratification debates (such as James Iredell of North Carolina) suggested an additional criterion of republicanism: absence of a titled aristocracy. This criterion was not part of the consensus, however, because other participants observed that some previous republics (e.g., pre-imperial Rome) and some contemporary republics (e.g., Holland) featured titled aristocracies. Indeed, the most influential contemporary foreign political writer, Baron de Montesquieu, divided republics into aristocracies and democracies. To assure, therefore, that the American states remained more purely democratic republics, the drafters of the Constitution inserted Article I, Section 10, which forbids states from conferring titles of nobility.

It is sometimes claimed that the Founders wanted American governments to be “republics rather than democracies,” but this claim is not quite accurate. As noted above, some dictionaries defined “republican” as “placing the government in the people” and writers such as Montesquieu and Ephraim Chambers considered a democracy as merely one form of republic. Leading Founders similarly employed the terms “democracy” and “republic” with overlapping or even interchangeable meanings. Although it is true that many of the Framers recoiled against the excesses of legislative democracy during the period prior to the Constitutional Convention, nonetheless in principle, only one species of democracy was deemed inconsistent with republicanism. This was “pure democracy” or “simple and perfect democracy,” a theoretical constitution identified by Aristotle and mentioned by John Adams and James Madison, among others. A pure democracy had no magistrates, because the “mob” made all decisions, including all executive and judicial decisions. The Founders saw this kind of democracy as inconsistent with republicanism, because it did not honor the rule of law. The Guarantee Clause’s protection against domestic violence assures orderly government and the rule of law, and protects the states’ legitimate magistracy against mob rule.

The primary purpose of the Guarantee Clause, however, was not protection against pure democracy but against monarchy. Based on precedents in ancient Greece, the drafters feared that kings in one or more of the states would attempt to expand their power in ways that would destabilize the entire federation. They believed that having a republican government in each state was necessary to protect republican government throughout the United States.

There is not much federal case law on the Guarantee Clause, primarily because in the 1849 case of Luther v. Borden, the Supreme Court declared in dictum that enforcement of the clause is a political question for Congress and not a justiciable issue for the courts. With one minor deviation, the Court has continued to adhere to this doctrine. Examples are the Court’s decisions in Pacific States Telephone & Telegraph Co. v. Oregon (1912) and Baker v. Carr (1962). Thus, citizens of a state who believe their state government is no longer republican should apply to Congress for relief rather than to the courts. Congressional control over what is a “republican form” is seen in the congressional admission of a state to the union, which legally implies that the state’s then-existing constitution satisfies the Guarantee Clause. Yet the clause does not freeze that state constitution into place, but allows states wide latitude to innovate, so long as they retain the three basic elements of the republican form.

There has been somewhat more Guarantee Clause activity in state courts. Most have arisen when opponents of direct citizen lawmaking (initiative and referendum) argued that it violated the “republican form” for voters to legislate directly rather than through representatives, even though early in our history states often passed resolutions instructing their representatives on how to vote on certain issues. The Delaware Supreme Court accepted that argument in Rice v. Foster (1847). However, numerous citations from the founding era indicate that this argument is erroneous, and it has been rejected entirely or in part by all other state courts considering the issue. Examples include the supreme courts of Colorado, Bernzen v. City of Boulder (1974) and other cases; of Washington, Hartig v. City of Seattle (1909); and of Oregon, Kadderly v. City of Portland (1903).

The other portion of the clause declaring that the United States shall protect each state “against invasion” was designed by the Framers to prevent a sectional president from refusing to defend certain parts of the nation from foreign attack. As St. George Tucker noted in his Blackstone’s Commentaries (1803), the provision guarded against “[t]he possibility of an undue partiality in the federal government in affording it’s [sic] protection to one part of the union in preference to another, which may be invaded at the same time.” There has been, however, no occasion when that section has been invoked.