The division of tax room for shared tax bases, such as income taxes in Canada, the United States, Australia, and Switzerland, is a frequent cause of political conflict between national and sub-national governments. Economists and legal scholars have developed a theory that sets out an optimal division of tax room, but federal nations often substantially depart from this prescription by allocating too much or too little tax room to national governments. This article argues that the divergence between theory and actual practice can be partially explained by a ‘credit assignment problem’ that affects the political economy of government decision making. To illustrate, the article develops a model to identify the incentives governments face when dividing tax room. The model’s central observations are that (a) the optimal division of tax room requires robust intergovernmental contracting, but (b) the necessary contracts are difficult or impossible to perform due to problems in allocating political credit – electoral rewards and punishments – between the two levels of government. The result is political conflict and, frequently, a sub-optimal division of tax room and the revenue that results. This article argues that law can perform two functions in responding to the credit assignment problem: (a) it can facilitate credit assignment, so that the necessary contracts over tax room and revenue are politically feasible, and (b), failing perfect credit assignment, it can mitigate the welfare effects of a sub-optimal division of tax room. The article shows how a credit assignment perspective should lead to reconsideration of constitutional law doctrines, such as the federal spending power and various doctrines that enable or limit concurrent expenditure jurisdiction. While these doctrines are the subject of long-running debates in legal scholarship, the credit assignment perspective offers new insights and new doctrinal prescriptions.

中文翻译：

---

重新思考财政联邦制中的税室和收入划分

共享税基的税收空间划分，例如加拿大、美国、澳大利亚和瑞士的所得税，是国家和地方政府之间政治冲突的常见原因。经济学家和法律学者提出了一种理论，提出了税收空间的最佳划分，但联邦国家经常通过向国家政府分配过多或过少的税收空间而大大偏离了这一规定。本文认为，理论与实际实践之间的差异可以部分解释为影响政府决策的政治经济学的“信用分配问题”。为了说明这一点，本文开发了一个模型来识别政府在划分税室时面临的激励措施。该模型的核心观察结果是：(a) 税室的最佳划分需要强有力的政府间合同，但 (b) 由于在两个级别之间分配政治信用——选举奖惩——的问题，必要的合同难以或不可能履行政府的。其结果是政治冲突，并且经常是税收空间和由此产生的收入的次优划分。本文认为，法律在应对信用分配问题时可以发挥两种作用：（a）它可以促进信用分配，因此税收空间和收入的必要合同在政治上是可行的，以及（b）在完美的信用分配失败时，它可以减轻税室划分次优的福利效应。这篇文章展示了信用分配视角应该如何导致对宪法学说的重新考虑，例如联邦支出能力和启用或限制并行支出管辖权的各种学说。虽然这些学说是法律学术长期争论的主题，但学分分配的观点提供了新的见解和新的教义规定。