On Tuesday, the Supreme Court will hear arguments tempting it to plunge into an impenetrable political thicket. It will consider a lower court’s ruling that, if allowed to stand, will require the judiciary to determine whether and when partisanship in drawing electoral districts — something as old as the Constitution — is unconstitutional. And courts will wrestle repeatedly with cases requiring them to decide how to decide how much partisanship is too much.

It is instructive that the phrase “partisan gerrymandering” — the drawing of district lines by one party to disadvantage the other — is a redundancy. It has been since 1812, when Massachusetts Democratic-Republicans, serving Gov. Elbridge Gerry, created a district resembling a salamander. By then, the practice was old hat for New York, which had been hard at it since 1788, the year the Constitution was ratified.

The practice has recently become hotly disputed. This is partly because Republicans control 66 of 98 partisan state legislative chambers, and both the legislatures and governorships of 26 states. (A challenge to Maryland’s redistricting by Democrats is percolating in the judicial system.) And it is partly because some members of the political science professoriate, which is as ideologically monochromic as academia generally, are inventing metrics that supposedly provide objective standards for identifying partisanship that is unconstitutionally excessive.

For several decades, federal courts produced redistricting plans for Wisconsin after decennial censuses because the Legislature could not agree on any. In 2010, however, Republicans won control of both houses of the Legislature and the governorship and produced a redistricting plan. In 2012, they won 60 of the 99 state Assembly seats with 48.6 percent of the statewide vote, and in 2014 they won 63 seats with 52 percent of the vote. However, under the court-devised plan in the previous decade, in five elections the Republicans won an average of 55.2 seats with an average of 49.1 percent of the statewide vote. This is partly because under requirements of the Voting Rights Act, Milwaukee’s “majority-minority” districts were protected. And it is partly because Democratic voters, in Wisconsin and nationally, are inefficiently distributed, disproportionately concentrated in cities and college towns, such as Milwaukee and Madison. This is why in 2012, Barack Obama carried 27 congressional districts with at least 80 percent of the vote, whereas Mitt Romney carried only one that lopsidedly.

The 12 plaintiffs against the Republican plan have three problems, each fatal. First, they are contesting the entire statewide plan rather than their individual districts. So, they are asking the court to change its traditional standards for “standing” to sue, which require persons to demonstrate a “particularized injury” — in this case, that the configurations of (BEG ITAL)their individual districts somehow unconstitutionally devalue their votes. The lead plaintiff is a retired University of Wisconsin professor whose Assembly district in Madison has voted Democratic by an average of 67.2 percent in the last five elections. This does not sadden him. What does — his supposed injury — is that the statewide plan diminishes his chances of enjoying a Democratic majority in the Assembly.

Second, until 31 years ago, the court held that the inevitable political component of redistricting plans is a non-justiciable “political question” properly consigned to the political (elected) branches. In 1986, the court said a political gerrymander could conceivably be justiciable, but it has never discovered what Justice Anthony Kennedy terms “a manageable standard.”

Third, the plaintiffs want the court to plunge the judiciary into unending litigation involving dueling professors who will cherry-pick concocted metrics to serve as standards. Tuesday’s arguments will illustrate why Wisconsin warns about a “social science hodgepodge.” Plaintiffs will argue that an “efficiency gap” (the difference between all the loser’s votes and the surplus of votes in excess of those the winner needed for victory divided by the total number of votes cast) that exceeds 7 percent — a figure plucked from the ether — is presumptively unconstitutional. By this metric, one-third of all legislative redistricting maps in 41 states over 43 years were impermissibly partisan.

Using partisan social science, the plaintiffs are asking the court to find in the Constitution a hitherto unnoticed requirement for proportional representation. Justice Felix Frankfurter perhaps anticipated this.

When in 1962 the court first intervened in states’ redistricting practices, it propounded only the simple and neutral principle of “one person, one vote” — districts must be numerically equal. Nevertheless, Frankfurter dissented, having warned in 1946 against even entering “this political thicket.” He worried that someday the court might be drawn ever-deeper into the fraught business of fine-tuning political processes. Unless the court is careful, that someday could arrive Tuesday.

© 2017, Washington Post Writers Group