Import-Export Tax Idea Presents State Constitutional Pitfalls

States could run afoul of the Constitution by following a federal border-adjustments plan advocated by House Speaker Paul D. Ryan (R-Wis.) to tax imports and exempt exports.

The commerce clause, and even the equal protection clause, could factor in how states respond to whatever bill is finally presented by Ryan and other congressional members.

Border adjustments, part of Ryan’s broader tax blueprint, haven’t yet been introduced in the House. President Donald Trump has said he thinks they are “complicated,” but hasn’t said he opposes the idea.

Many details are unclear, such ...