Today the Supreme Court heard oral argument in two redistricting cases, one challenging state legislative districts in Virginia and the other congressional districts in North Carolina. Both cases challenge choices made by redistricting state legislators in response to the prevailing interpretation of the Voting Rights Act of 1965. "The claim made by [lawyers purporting to represent] black voters in both states," the Associated Press reports, "is that Republicans created districts with more reliably Democratic black voters than necessary to elect their preferred candidates, making neighboring districts whiter and more Republican."

The prevailing interpretation of the Voting Rights Act has been that redistricters are required to maximize the number of "majority-minority" districts. The idea is to stop the spreading out of black voters into multiple districts where they would be outnumbered by whites; the theory is that whites would oppose the election of legislators who took positions favored by most blacks. The partisan effect, given that overwhelming majorities of blacks tend to vote Democratic and smaller majorities of whites tend to vote Republican, has generally been favorable to Republicans, because corralling blacks into a few districts tends to make the larger number of adjacent districts more Republican.

Both parties figured this out some time ago. A FiveThirtyEight.com article gets the history wrong when it states, "In the 1990s, Republicans fought back against Democrats' efforts to create more minority-controlled districts." Nope: I remember being in Tallahassee in the early 1990s, when Democrats held the Florida governorship and majorities in both houses of the legislature, and Republicans put together a coalition with black Democratic legislators to increase the number of black-majority (and Hispanic-majority, in Miami-Dade County) congressional and legislative districts. Republicans in other states then, and much more so after the redistrictings following the 2000 and 2010 Censuses, employed similar tactics.

Such districting, by the way, is almost entirely responsible for the grotesquely shaped districts cited by redistricting "reformers" who want to consign redistricting to supposedly non-partisan commissions (which usually get gamed successfully by Democrats, as happened after the 2010 Census in California and Arizona).

The two cases the Supreme Court is considering were both brought by Democrats who want to keep the requirement of maximizing majority-minority districts but make it work for the partisan interests of the Democratic rather than the Republican party. Their arguments, as relayed sympathetically in the FiveThirtyEight.com article, are that keeping the black majorities down in majority-minority districts would tend to produce legislative outcomes favored by black voters. In other words, the Constitution and the Voting Rights Act should be interpreted as requiring that Democrats win more legislative elections than they currently do. That's what justices will be doing if they require federal judges to guess whether redistricters have drawn districts with "more reliably Democratic black voters than necessary to elect their preferred candidates."

The fact is that politics cannot be kept out of redistricting (even in supposedly non-political commissions). But strict application of the equal-population standard limits, and rather more strictly than redistricting critics suggest, the partisan advantage that redistricters can give their party. If you create too many 53 percent districts for your side, you may find it losing its majority when voters switch 5 points to the opposition.

What should the Supreme Court do? If it wants to maintain the requirement of maximizing the number of majority-minority districts, it shouldn't put the courts in the business of adjudicating just how large those majorities should be. That's a political judgment, and it should be left to the politicians. Remember that redistricting isn't forever. The lines have to be redrawn every 10 years and can be redrawn in the interim.

Another course would be to rule that the prevailing interpretation of the Voting Rights Act is wrong, and that a districting plan with equal-population and contiguous districts will not be overturned because it gives the redistricting party a marginal advantage. I don't expect the Supreme Court to do that, but I think an argument could be made for it — and it would get the courts out of the redistricting thicket.