Congressional Republicans, traditional defenders of states’ rights, will deliver an unexpected one-two punch to state tax systems if the current version of their tax bill becomes law as expected.

The tax plan, negotiated behind closed doors, includes an expansion of 529 savings accounts and the partial elimination of state and local tax deductions. These changes will provide new avenues for people to avoid state income tax that states never envisioned. And those states will have a hard time making up the difference.

The first blow would come from expanding 529 college savings accounts, which offer tax advantages to encourage families to save money for college, to cover K-12 expenses, such as private school tuition and home schooling costs.

This amendment by Senator Ted Cruz passed only because of a midnight tiebreaking vote cast by Vice President Mike Pence. Under current law, earnings on contributions to 529 plans are not subject to federal taxes. These investment vehicles work well for college savings because deposits grow tax-free over a long time. Using 529 accounts for elementary or high school tuition, however, substantially shortens that period, making these accounts a minimal boost to school choice.