Barton Gellman in The Atlantic on the potential implications of Moore v. Harper for presidential elections (if, a big if, any independent state legislature holding in the congressional election context extends to presidential elections, too).

To understand the stakes, and the motives of Republicans who brought the case, you need only one strategic fact of political arithmetic. Six swing states—Pennsylvania, Michigan, Wisconsin, Arizona, Georgia, and North Carolina—are trending blue in presidential elections but ruled by gerrymandered Republican state legislatures. No comparable red-trending states are locked into Democratic legislatures. . . .

If you give the legislature a blank check on the manner of appointing presidential electors, then a Republican majority could—in the most muscular version of ISL—simply disregard a Biden victory in the state’s popular vote and appoint Trump electors instead. . . .

But if the Supreme Court adopts the ISL doctrine in Moore, the argument that Texas made will become a model in 2024. The conditions that Texas cited in its argument are almost always present in contemporary elections. Legislatures pass laws on the conduct of the vote, but election administrators have to interpret those laws and set implementing rules such as precinct locations, polling times, and counting procedures. State courts sometimes mandate changes in the rules to comply with their state constitutions. It’s all but impossible to conduct an election without making rules or choices that the legislature did not specifically authorize.

The pernicious threat of ISL, wrote Richard L. Hasen, an election-law expert at UCLA, is that “a state legislature dominated by Republicans in a state won by Democrats could simply meet and declare that local administrators or courts have deviated from the legislature’s own rules, and therefore the legislature will take matters into its own hands and choose its own slate of electors.”