This week, Blaine Saito (Ohio State, Google Scholar) reviews a new work by David Gamage (Missouri, Google Scholar) and Darien Shanske (UC Davis, Google Scholar), Against Doctrinal Siloing: Harmonizing Fiscal Federalism and the U.S. Constitution, 103 Wash U. L. Rev. _ (forthcoming 2026).

Fiscal federalism is embedded within the U.S. constitutional structure dating back to the founders. Over time the Supreme Court has developed numerous tests and doctrines to balance fiscal powers and responsibilities between the federal government and the states. But these doctrines are a messy jumble. Fiscal federalism is different under the commerce clause when Congress legislates, the dormant commerce clause, state sovereign immunity, the spending clause, section 5 of the Fourteenth Amendment, and the taxing clauses of apportionment of direct taxes and uniformity of excises, imposts, and duties. The result is what one could charitably call a doctrinal hot mess. In their essay, Against Doctrinal Siloing: Harmonizing Fiscal Federalism and the U.S. Constitution, David Gamage and Darien Shanske draw on the concept of proportionality to develop a useful balancing framework that works to harmonize these doctrines and in many ways engender clearer reasoning and discussion of how these two sovereign realms must act in the fiscal space. They thus provide a means to resolve today’s fiscal federalism conflicts beyond just digging through eighteenth-century history to find answers for our twenty-first-century digital economy, while remaining true to a great deal of the Framers’ intentions.

Gamage and Shanske draw on the concept of proportionality, which appears in U.S. law, but is more commonly associated with German and E.U. law. The basic concept is that when there are two conflicting rights, something must give. But it should only give to the extent that it is proportional to resolve the conflict rather than completely choosing one right over the other. They propose the Federal Fiscal Proportionality Review (FFPR). This framework helps to harmonize the doctrines in the disparate federal fiscalism areas. It is also a rebuttably presumptive framework. The FFPR acknowledges that while proportionality is the best way to handle clashing principles, it cannot override a specific, unambiguous textual command. For example, the Constitution’s age requirement for the Presidency cannot get overridden through proportionality review.

The framework has four key parts. One evaluates: “(1) asserted federal interest; (2) the state interest at stake; (3) whether there is reasonable tailoring between means and ends; (4) whether the federal benefit is proportional to the burden on state autonomy.” The key part of the test is looking then at how narrowly tailored the matters are and the proportionality that arises. The framework, in many ways, echoes parts of current doctrine in these disparate areas. Additionally, FFPR helps designers focus on how to calibrate measures to ensure that the rights of the two sovereigns are in balance. It rejects the idea that everything must be an all-or-nothing victory for one sovereign or the other and thus provides a textured and nuanced approach.

The authors then show first how this applies to limits placed on state revenue power. One key example is how it would apply to the morass of the dormant commerce clause doctrine. The authors take FFPR and apply it to the Maryland digital advertising tax, which applies only to an advertiser with at least $100 million in gross receipts in Maryland. No Maryland-based company is subject to this tax. On the first prong, the federal interest is to preserve the national market. The state has an interest in raising revenue related to its consumer base. When it comes to the tailoring analysis, it is true that the tax affects only out-of-state businesses. But it is not really seeking to do that in any substantive way, even by proxy. That helps limit the federal concerns of the national market and discrimination. Finally, on the fourth part, there is nothing here that smells of protectionism for Maryland companies. As a result, it avoids contravening the fundamental federal interest in maintaining a unified national market free from state-erected economic barriers. Of course, if the tax were designed differently with certain carve-outs, that would and should change the proportionality calculus. Design details then are important.

Gamage and Shanske then turn to the limits on the federal taxing power. The FFPR clarifies the categories of direct taxes subject to apportionment and duties, imposts, and excises subject to uniformity. Once classified, FFPR also helps to assess the validity of apportionment measures or uniformity.

When it comes to classification, FFPR helps to protect the fiscal autonomy interest states have. That idea, which comes from both Justice Thomas’s Moore v. United States dissent and the arguments of Professors David Schizer and Steven Calabresi, is based on the concept that the direct tax apportionment language is meant to ensure interstate equality and prevent the federal government from raiding the states. The third and fourth parts of the FFPR help to provide a useful analytical hook rather than having it be a somewhat arbitrary labeling exercise.

To get that point across, Gamage and Shanske provide a comparison between two taxes, a federal wealth tax on all wealth over a threshold amount regardless of how it is held and a federal levy on commercial oil and gas reserves. Both have clear federal and state interests at stake. But for a wealth tax, when looking at tailoring and proportionality, it seems well-tailored and proportional to the interest. Few states tax all wealth, especially the intangible wealth that is highly mobile and makes up the largest share of the wealthy’s holdings. On the other hand, when looking at the oil and gas levy, those impinge much higher on state interests, and thus, mean that apportionment may make more sense to allow for proper tailoring and prevent interstate inequities. Similar inquiries then can be made as to whether something meets apportionment or uniformity depending on the categorization.

Overall, the essay helps to clean up doctrinal messes in fiscal federalism. The FFPR also is useful in another way. In engaging in the proportionality analysis and weighing interests, the FFPR really aims to look at how values interact with one another and how we make tradeoffs workable. The other advantage that the authors do not mention then about the FFPR is that it not only cleans up doctrine, but it makes these value arguments more legible. In doing so, it not only helps courts provide better reasons, but it also allows political actors and the administrative state at both the federal and state levels to articulate their own values and to think carefully about tailoring those conflicts together. Highlighting that too not only enhances federalism, but overall deliberation that is key to our federal system and democracy. In that way too, the FFPR also serves as a light toward helping us better engage with these thorny issues not just in court, but in our public discourse.

Here’s the rest of this week’s SSRN Tax Roundup:

Daniel J. Hemel (NYU), Taxation and Animals, 77 Case Western L. Rev. _ (forthcoming 2026)

Fabian Kratzlmeier (Max Planck Institute), The Tax Creditor Under European Insolvency Law: Special Treatment, Equal Treatment, or Even Worse? (May 13, 2026)

Daphna Lewinsohn-Zamir (Hebrew U.) & Ilana Ritov (Hebrew U.), Harnessing the Identifiability Effect to Enhance Public Support for Redistribution, J.L. & Empirical Analysis 153 (2026)

Surrender Naik Maloth, Legal and Tax Considerations for Starting a Business: A Comparative Study of Germany, India, and the United States (May 11, 2026)

Daramola Joseph Omoyele (Independent), Tariff Threats and Digital Tax Sovereignty (May 11, 2026)

Katherine Pratt (Loyola L.A.), Aligning Reparations and Taxation, 32 William & Mary J. Race, Gender & Social Justice 395 (2026)

Diane M. Ring, Assessing Decision-Making in Global Tax Organisations: A Research Agenda, 2025 British Tax Rev. 61

Tamir Shanan (College of Management, Israel) & Doron Narotzki (Akron), Taxation of Cross Border Migrations: Re-evaluating the Allocation Between Home Country and Host Country, in Fairness in International Taxation (Ira K. Lindsay & Binu Mathew, eds. 2025)

István Simon (Eötvös Loránd U.), Cryptocurrencies in National Laws – Hungary (May 8, 2026)

Donald B. Tobin (Maryland) & Alex Tobin (Independent), Living Constitutionalism, Originalism, and the Sixteenth Amendment, 77 Ala. L. Rev. 511 (2026)

Steven Utke, Closing the Carried Interest Tax ‘Loophole’ Could Raise $90 Billion over 10 Years . . . If the Difference Between Ordinary and Capital Tax Rates Exceeds 50% (May 11, 2026)

Manoj Viswanathan (UC Law SF), Toward Issuer-Based Certification of Qualified Small Business Stock (May 7, 2026)

Payal Wagh, Shadows of Justice: A Critical Analysis of Confidentiality, Accessibility, and Arbitrator Bias in International Tax Arbitration (May 9, 2026)