Taxes were already a big issue in the November elections. The Supreme Court just made them an even bigger one.

The Supreme Court’s decision on taxing offshore earnings could have been an indirect, though significant, move in the fight over wealth taxes — but it didn’t turn out that way.

The justices decided Thursday not to wade into the legality of taxing a household’s paper gains, emphasizing that their 7-2 decision was narrow and confined only to the provisions of the 2017 tax cuts at issue.

Both supporters and detractors of a wealth tax painted the decision as a glancing win for their side.

“The fight goes on to tax...