Besides their Western backgrounds and their justice-former clerk connection, Anthony Kennedy and Neil Gorsuch seem to have little in common in style and views. But in April, the two justices likely will align in the multibillion-dollar battle over state taxation of online retail sales.

In South Dakota v. Wayfair, set for argument April 17, South Dakota urges the justices to invalidate a 51-year-old rule that a business must have a physical presence in a state before that state can require it to collect sales taxes.