UNLIKE the democratic societies of ancient Greece, where every citizen had a direct role in the administration of the polis, the hallmark of modern democracy is representation, not participation. The mechanics of elections are thus critical to the operation of American democracy, and on December 8th the Supreme Court will consider a fundamental question it has elided in previous rulings: When states draw electoral districts, who should they consider to be the population that is being represented? Is it the eligible voters who count—a category that excludes non-citizens, children and felons, among others? Or is the total population—including people who are not eligible to vote—the right metric? The parties’ briefs in Evenwel v Abbott give the impression that the question may be best addressed in a university seminar room. The dispute in those pages has the air of a dry academic exercise, with few glimpses into the political issues involved. But to pick up the many amicus (friend-of-the-court) briefs on both sides is to see the centrality of the case to the real-world jockeying of America’s political parties. The stakes of Evenwel are potentially huge, and it appears that Democrats have the most to lose.

The lawsuit comes from Sue Evenwel and Edward Pfenniger, two Texans who complain that their state’s Senate district map puts them at a comparative disadvantage when entering the voting booth. Ms Evenwel and Mr Pfenniger live in Districts 1 and 4, respectively, and most of their neighbours are eligible voters. But in other Senate districts, the plaintiffs say, many fewer residents are eligible to vote. This means that voters in these parts of the state are, in Orwell’s terms, “more equal than others”. Using demographic data, the plaintiffs purport to show that their franchise is only about half as worthwhile as that of eligible voters in other districts. This amounts to a violation of the 14th amendment’s equal-protection clause, Ms Evenwel and Mr Pfenniger say, as the Supreme Court decided over 50 years ago that “an individual’s right to vote for state legislators is unconstitutionally impaired when its weight is in a substantial fashion diluted when compared with votes of citizens living in other parts of the State.”

That 1964 case, Reynolds v Sims,announced the principle of “one person, one vote”, a rule that says states must count “people” (rather than “trees or acres”) and distribute them relatively evenly (with a margin of error of 5% either way) when drawing district maps. But the Supreme Court has not been very clear about whether “people” means everybody, or just eligible voters. The plaintiffs in Evenwel say that Reynolds and other cases refer to the “people” as the body of individuals who are eligible to vote. “Texas breached [its] fundamental obligation in creating these Senate districts,” the appelants’ brief reads, and its “massive and arbitrary malapportionment of eligible voters is patently unconstitutional”. Turning to a rather implausible hypothetical scenario, the plaintiffs ask if Texas could adopt a map where “30 of the districts each contained one eligible voter and the 31st district contained every other eligible voter in the State”. A decision upholding such a lopsided arrangement, the brief says, “cannot be right” and must run afoul of the 14th amendment.

Texas offers a moderate response: states can do as they choose. It points to a case from 1966 in which the Supreme Court permitted Hawaii to count only eligible voters when drawing up its districting scheme. Since so many military personnel and seasonal tourists were coming and going into and out of the Aloha state, the Court ruled, it was fine for Hawaii to discount transients and deviate from total population when creating its district map. The plaintiffs say this case, Burns v Richardson, speaks in their favour. But Texas disagrees. Burns stands for the principle, the Lone Star state's brief reads, that states are free to choose any reasonable reference population it likes when determining district boundaries. “A state’s decision to include or exclude non-voters in its apportionment base ‘involves choices about the nature of representation with which we have been shown no constitutionally founded reason to interfere.’”

In other words: don’t mess with Texas. Or with any other state’s decision about how it would like to set up its electoral districts. As long as a state undertakes a good-faith effort to draw district lines and does not target specific populations for “invidious vote dilution”, its maps should be constitutionally kosher.

But interestingly, for many of the 21 amici lining up on the side of Texas, this live-and-let-live standard doesn’t go far enough. It would be a mistake, these groups say, to give states the option to use eligible voters as the districting metric. Total population is the only measure that is consistent with the Constitution’s promise of equal representation. The brief submitted by Brennan Centre, a think tank at the New York University law school, contends that “[a]pportionment based on total population...is deeply embedded in our Constitution, our nation’s history, and the longstanding actual practice of government.” It “ensure[s] a government of and for the people” and is a safeguard against “efforts to disadvantage unpopular or disfavoured groups”. History shows that “manipulation of apportionment rules...den[ied] equal representation to parts of states where African Americans in the South, Irish-Americans in Massachusetts, Mormons and Chinese in the nation’s western territories, and immigrants in New York City lived”.

The implications of a win for Ms Evenwel and her co-appellant may have a similar effect. The districts in Texas with a smaller proportion of eligible voters are home to many racial minorities. The brief from the NAACP points out that a turn away from equality of representation “will fall most heavily on black residents, immigrants and other communities that already face historical and contemporary discrimination.” Black communities in the United States include “20 million people who are not ‘eligible voters’” comprising “13 million black children, nearly 5 million non-registered black voters, 2 million black non-citizens and 2 million black individuals with felony convictions.” Since minorities tend to vote for Democrats, reorienting influence toward districts with higher concentrations of white voters like those where Ms Evenwel and Pfenniger live could give Republicans an electoral boost.

Amici arguing for the plaintiff take issue with this pat conclusion. The Cato Institute, for example, suggests that "eligible and ineligible voters of the same race" may often have conflicting "political preferences":

We can imagine, for example, a hypothetical heavily Hispanic state senate district in Texas. Suppose this district is a mix of nonvoting aliens, recently naturalized citizens, and second-or-third generation Americans of Spanish descent. On issues such as whether immigration queues to enter the country should be strictly enforced and the extent to which Texas should police its border with Mexico, can we assume the political opinions of everyone in each of these groups will be aligned? Or is it more plausible that a not-insignificant percentage of Hispanic citizens will vote on immigration issues in a way that is completely opposed to the interests of nonvoting Hispanics? If so, counting those alien Hispanics in the total for apportioning voting strength to the voting Hispanics near them may hurt their political interests in exactly the same way that counting nonvoting blacks in the apportionment of House members to be elected by southern whites would have harmed the interests of those nonvoting blacks.

That's an interesting thought experiment. At this point we can only speculate about the potential effects of a win for Ms Evenwel. Nine unelected judges hold in their hands a fundamental question of American democracy that could alter the political terrain for decades to come.