Yes, that's a hard-g in "gerrymandering," people. Elbridge Gerry. Hard-g.
Anyway, some definitions are in order because for most people, "gerrymandering" is just some generic evil, like fascism or hipsterism. There are actually three primary categories of gerrymanders, in most taxonomies. I say four, but I'm unmutual.
1) The racial gerrymander, which dilutes the voting power of a racial or ethnic group. Unconstitutional, sort of. The Voting Rights Act of 1965 requires that, where possible, lines be drawn to create majority-minority districts (which are districts in which a majority of the population is a racial or ethnic minority) because that is the only way minorities wind up in office since white people don't often vote for non-whites. On the other hand, the Supreme Court ruled, in Shaw v. Reno, that lines can't be drawn primarily on race. Since these requirements obviously contradict each other, the requirements on "racial gerrymanders" are actually kind of a mess, in terms of constitutional doctrine.
2) The bipartisan gerrymander packs Democratic voters into Democratic districts, and packs Republican voters into Republican districts. That way, Democratic incumbents win overwhelmingly in their districts, and Republican incumbents win overwhelmingly in their districts. There are no close districts. Your average goo-goo* hates these plans. I love them, and have published a bunch of stuff on the mathematical properties of these plans, particularly in relation to the competitive gerrymander (see below). Mostly, they give you a partisan balance closest to the electorate, ideological compositions that are best suited to the electorate (that one really surprises people), and done properly, actually prevent one party from locking in a big majority through a wave election that winds up combining uncomfortably with incumbency advantages. Think about that last one-- if the House is 217-217-1, then everything turns on 1 district. 435 competitive districts? One big wave election plus incumbency advantages and one party can lock in a long-term majority with the luck of timing. I went through the math on that in an old paper.
3) The competitive gerrymander. This is when you go out of your way to draw 50-50 districts. Most people don't call this a gerrymander. I do. You often have to draw crazy lines by doing things like chopping up cities to get this outcome, and that can be ugly. Any plan intended to achieve a political outcome is a gerrymander, and there are some negative representational consequences of 50-50 districts, as a lot of my research shows. But, I'm rambling. I'll get to the point...
4) The partisan gerrymander. This is what nobody (except the advantaged party) will ever really defend. A partisan gerrymander is a plan that gives a mathematical advantage to one party through a "pack-and-crack" system. It gets lumped in with the bipartisan gerrymander by people who just think of all gerrymandering as a generic evil, but that's the problem because the plan is very different. Bipartisan gerrymanders pack voters of each party into their own districts. Here's how a partisan gerrymander works:
One state, 33 voters, to be divided into 3 districts. 12 Republicans, 21 Democrats. Districts 1 and 2 get 6 Republicans each, and 5 Democrats each. District 3 gets 11 Democrats. Did you catch that? District 3 is "packed" with too many Democrats-- way more than they need to win. The remaining Democrats are "cracked" across Districts 1 and 2. With 10 remaining Democrats, that's enough to win another district, but not if they are spread like that. As a result of the pack-and-crack, 12 Republicans have a majority in 2 out of 3 districts, even though they have about 1/3 of the population. That's a partisan gerrymander.
The Supreme Court has a messy history with this one. They have ruled in the past that, in principle, there may be such a thing as going too far with a partisan gerrymander, but they have never actually struck down a redistricting plan for partisan gerrymandering. Last month, they came close-- they struck down a redistricting plan in North Carolina by recognizing that a partisan gerrymander was a racial gerrymander, so they could just use precedent on racial gerrymanders to strike down a partisan gerrymander. I posted about it briefly.
That hints at several of the issues here. First, why is a partisan gerrymander still considered constitutional?
Um, do you know how long it took before the Supreme Court struck down districts of unequal population? Baker v. Carr. 1962. Why? Well, if the Senate is based on state lines, and states are of unequal population, then obviously district lines don't need to be based on equal population. That sounds morally vile, but on constitutional grounds, you gotta admit-- it isn't completely groundless. Evil, yes, but the Constitution isn't a moral document. It enshrined slavery, for fuck's sake! Then, and here's something everyone forgets-- go read the Constitution. Where does it say you have a right to vote?
Nowhere. It gives you some reasons that you can't be denied that right, but there is no positively stated right.
You start to see the problem. From a moral standpoint, it is easy to look at a partisan gerrymander and find it vile. From a constitutional standpoint, finding grounds to strike down any given plan has always been problematic. In the recent North Carolina case, the SCOTUS found a way-- use race and the inseparability of party and race. Now, it is still the case that majority-minority districts pack Democrats inefficiently into their districts, and that benefits Republicans. As long as that happens, Republicans have an advantage, and I'll get to that, but North Carolina Republicans pushed it too far.
Anyway, though, the Supreme Court is now taking up a case in Wisconsin that isn't about race. It is a straight-forward partisan gerrymander case.
What will they do? Well, where things get messy is in the implications. Redistricting plans always have competing goals. The VRA issue is just one example, but the basic point is that any plan that has a partisan bias can be defended on other grounds. Keeping "communities of interest" together, i.e. not chopping up cities (where most minorities live anyway) in ridiculous ways, will keep Democrats packed into their districts because Democrats cluster more in cities. That type of thing benefits Republicans. A Supreme Court ruling could, in principle, put a limit on what states do, depending on what they are willing to say, and how far they are willing to go, but we don't know that.
Having already taken away the race-partisanship excuse in the North Carolina case, states are more limited in what they can argue, and I won't hazard a guess at the outcome here. But, I'm a cynic about the Supreme Court, and legal thought in general. I tend to think of the field as one big exercise in motivated reasoning, where they start from an outcome, and then reverse-engineer an argument to get them to where they want to go. If five justices decide that they want to start limiting partisan gerrymanders, they'll find a way to do it. Hell, on the ACA a couple of years ago, Roberts decided that the individual mandate was not a tax, therefore anti-injunction didn't apply, and he could review it before it went into effect, but as soon as that happened, it became a Schroedinger's cat type of thing, changed with observation, became a tax, and therefore became constitutionally defensible under Article I as a tax rather than under interstate commerce, but only after being observed as not a tax so that he could get around anti-injunction. Did'ya follow that? Why did Roberts not want to strike down the ACA? Who the fuck knows? But, with a chain of reasoning that convoluted, you know it's motivated reasoning. They do that kind of shit all the fucking time. They twist themselves into knots to get to their chosen outcomes, and they will do that here. What will they argue? It depends on where they want to go, which I don't know.
Remember, there is no constitutional right to vote. Should there be? If I were writing a constitution, I'd include one. Partisan gerrymanders? Yeah, they suck. What will SCOTUS do? Twist themselves into knots to get their chosen outcome. They've been reluctant to strike down partisan gerrymanders before, but hey, they sort-of got there with North Carolina. Maybe they'll go all the way this time.
*Infantilizing term for good government advocate. Since they are infants, they should be infantilized.