In a 5-4 decision along party lines, the U.S. Supreme Court on Monday upheld an Ohio law that lets the state kick people off the voter rolls if they don't show up to vote for six years and don't return a postcard saying they haven't moved.

It would be nice if legal principle had played any role in the decision on either side, but it didn't, not really. The five conservatives, including Justice Anthony Kennedy, found in Husted vs. A. Philip Randolph Institute that the state law was consistent with federal law; the four liberals said it wasn't.

Like the Republican state legislature that passed the law, both sides are apparently operating on the unspoken assumption that Democrats are more likely to decide not to vote and fail to return the postcard than are Republicans. No matter which side you think is correct, the partisan breakdown on a voting rights case is not a great look for the justices.

The legal background for the decision is a federal law, the National Voter Registration Act of 1993, that sends two arguably conflicting messages to the states. On the one hand, the federal law says that the states must make a "reasonable effort to remove the names of ineligible voters" who have changed their residences. On the other hand, the same law tells the states that they can't take away anyone's voter registration "by reason of the person's failure to vote."

One way for states to satisfy these legal obligations is to target people for removal from the voting rolls if they have filed a change of address notice with the U.S. Postal Service that moves them into a new voting district. Ohio does this. But apparently, 40 percent of people who move don't submit a change of address notice.

The Ohio law addresses this reality by adding another method of purging the rolls. If you don't vote for two years, then the state sends you a postcard asking if you are still there. If you reply that you haven't moved, you stay registered.

If you don't send back the postcard, then the state waits four more years, a period that must include two federal elections. Once a total of six years has passed since the first election you missed, Ohio takes away your registration.

You don't have to have gone to law school to guess how the two sides reasoned out the conclusion. Writing for the conservative majority, Justice Samuel Alito argued that Ohio's approach doesn't remove anyone "by reason of" the failure to vote. Nonvoting is just the trigger that begins the process, plus a factor in determining whether the person still lives where he or she is registered. The postcard, he maintained, is a form of notice that also helps makes the whole process about more than just removing voters who don't turn out.

For good measure, the federal law also says expressly that the state can't remove you unless you haven't responded to a notice and haven't voted in two straight federal elections. Alito used this restriction to conclude that if you have received the notice and haven't voted in two straight elections, you can be removed.

Justice Stephen Breyer went the other way. He focused on nonvoting as the triggering event for sending the notice in the first place. That, Breyer reasoned, amounted to removing you for failing to vote — precisely what federal law prohibits.

If you really wanted to, you could try to claim that Alito's opinion focuses on the literal meaning of the words "by reason of," and that Breyer's opinion focuses on the purpose of the federal law, namely not taking away people's registration for not voting. That would give some color of jurisprudential principle to the outcome here.

In the past I've often pointed out in this column that the court's conservatives interpret statutes based on text, while the liberals, especially Breyer, prefer looking to statutory purpose. But in this instance, Alito acknowledged looking to "context" to resolve the meaning of the words "by reason of." And Breyer claimed his view was required by the text of the federal law.

So the best, albeit unfortunate, conclusion is that the justices are just being political. I have no idea if they are correct about the partisan effects of the Ohio law or if they are just basing themselves on the same prejudices that informed the state legislature. But none of that should really matter. Partisanship should not inform statutory interpretation in this way.

I also don't think there's any way to read the tea leaves of this opinion to tell us anything about what Justice Kennedy will do on the partisan gerrymander case yet to be decided this term. He could be throwing a bone to the conservatives here because he plans to hold that some partisan gerrymanders are unconstitutional. (That's what I expect him to do.) Or he could be voting with his sometime partisan allies here and in that other case. We'll know soon enough.