The debate over eliminating the federal tax deduction for state and local taxes — a linchpin of the Republican tax cut plans now working their way through Congress — has focused on the economic and political effects of the change. But that may be the wrong discussion. The question is whether eliminating the deduction is even constitutional. History suggests that it’s not.

The most cogent analysis of this issue comes to us from the grave — specifically, from the late Sen. Daniel Patrick Moynihan (D-N.Y.). Moynihan addressed the issue in a 1985 speech, later published in the political science journal Publius.