Guaranty Clause cases are routinely tossed on the grounds that they raise a "political question" that courts should not decide. Last week, however, Judge William Martinez rejected that argument and ruled that this case can proceed. The ruling breaks new ground.

Courts steer clear of the Guaranty Clause because no one quite agrees what a "republican form of government" is. Even today, we can rule out governments with kings, but Saddam Hussein's Iraq was a "republic," as is Kim Jong-un's North Korea. James Madison, that font of wisdom, defined a republic in Federalist 10 as "a government in which the scheme of representation takes place," as distinct from "a society consisting of a small number of citizens, who assemble and administer the government in person." Direct democracy, by this definition, would be anti-republican. Sounds good, but it was Madison's own notion, rather than a standard definition.

In 1849, when Rhode Island was in the middle of a small civil war, the Supreme Court refused to use the Clause to decide which of the two warring governments was valid. That duty, it said, fell to Congress, which would seat the representatives of the government it found legitimate. At the dawn of the twentieth century, many scholars argued that the so-called "Oregon system" of initiative, referendum, and recall was anti-republican. In 1911, the Supreme Court rejected a challenge to Oregon's initiative system by a corporation that objected to paying taxes adopted by popular vote. The tax itself was a perfectly ordinary tax, the Court pointed out; the company's argument was simply that it had to be adopted by a different mechanism. Congress might have a right to outlaw the initiative, the Court said, but the courts did not. "It follows that the case presented is not within our jurisdiction."

Perhaps for that reason, the state of Colorado responded to the latest lawsuit as if it were a frontal assault on the initiative itself. "[T]his case is an effort to have the courts remove what [plaintiffs] see as an obstacle to their policy agenda: direct citizen participation in lawmaking," the state's motion to dismiss argued. Robert Natelson, a former constitutional law professor at the University of Montana, bolstered the state's arguments in an amicus brief for the conservative Independence Institute. The brief argued that the term "republic" at the time of the Founding embraced many ancient systems -- such as Athens and Sparta -- where citizens directly made the laws.

But Judge Martinez, who was appointed to the bench in 2010, held that the Colorado case isn't a challenge to the adoption of law by initiative. It is, rather, a challenge to a specific system of government -- however adopted -- wherein there is effectively no delegated power to tax. Thus, he said, the Oregon case did not bar the court from at least hearing the case. "This action . . . seeks not the invalidation of Colorado's ballot initiative system. Plaintiffs, in fact, seek only to invalidate one particular measure passed via the Colorado voter initiative process: TABOR." Invalidating that measure, if it happens, "will in no way affect Colorado voters' power of initiative . . . ."