Federalism, Supremacy, Preemption, the Dormant Commerce Clause, and Privileges & Immunities
Key Takeaways
- The Supremacy Clause makes valid federal law supreme; preemption may be express, field, or conflict (impossibility or obstacle) preemption.
- The Dormant Commerce Clause bars state laws that discriminate against or unduly burden interstate commerce even where Congress has not acted.
- A state law that facially discriminates against interstate commerce is almost per se invalid unless it serves a legitimate local purpose with no nondiscriminatory alternative; nondiscriminatory laws get the Pike balancing test.
- The market-participant exception lets a state favor its own residents when the state is buying or selling rather than regulating.
- The Privileges and Immunities Clause of Article IV bars discrimination against out-of-state citizens regarding fundamental rights (livelihood) and does not protect corporations or aliens.
The Presumption Against Preemption and Reading the Statute
Before cataloging the types of preemption, fix the analytic starting point: because the states are independent sovereigns, courts apply a presumption against preemption in fields the states have traditionally occupied (health, safety, family law, property). The 'ultimate touchstone' of every preemption case is congressional intent, gathered from the statute's text and structure. A federal savings clause that expressly preserves state remedies cuts strongly against preemption, while an express preemption clause is read no more broadly than its language requires.
Keep separate the question of Congress's power to preempt (it plainly has it under the Supremacy Clause whenever acting within an enumerated power) from the question of whether it actually intended to displace the particular state law before you. Most exam errors here come from assuming preemption follows automatically from the mere existence of overlapping federal regulation; it does not — overlap alone is not conflict, and a state may often regulate alongside or more stringently than the federal floor.
Supremacy and the Three Types of Preemption
The Supremacy Clause (Article VI) makes the Constitution, federal statutes, and treaties the 'supreme Law of the Land,' binding state judges notwithstanding contrary state law. When state and federal law collide, federal law preempts. There are three preemption theories:
- Express preemption — a federal statute expressly states that it displaces state law. Courts read express preemption clauses narrowly, with a presumption against preemption in fields traditionally regulated by states.
- Field preemption — Congress intends to occupy an entire field, inferred from a pervasive federal regulatory scheme or a dominant federal interest (e.g., immigration, nuclear safety, foreign affairs). State law in the field is displaced even without an actual conflict.
- Conflict preemption, which has two branches: impossibility preemption (it is impossible to comply with both federal and state law simultaneously) and obstacle preemption (state law stands as an obstacle to accomplishing the full purposes and objectives of Congress).
A classic MBE trap: a state law that sets a higher standard than a federal floor is usually not preempted unless the federal scheme intends uniformity or a ceiling. Conversely, a state law that frustrates a deliberate federal balance is preempted under the obstacle theory. Always anchor preemption in congressional intent.
The Dormant Commerce Clause
Even when Congress has not legislated, the Commerce Clause has a 'dormant' or negative aspect that restrains states from burdening interstate commerce. The analysis turns first on discrimination:
| State Law Character | Standard |
|---|---|
| Facially discriminates against out-of-state commerce (protectionist) | Virtually per se invalid; survives only if it serves a legitimate, non-economic local purpose (e.g., health/safety) with no less-discriminatory alternative |
| Nondiscriminatory but burdens interstate commerce | Pike balancing: invalid if the burden on interstate commerce is clearly excessive relative to the putative local benefits |
Philadelphia v. New Jersey struck a ban on importing out-of-state waste as facial economic protectionism. Pike v. Bruce Church supplies the balancing test for evenhanded regulations. Two key exceptions allow otherwise-invalid discrimination:
- Market participant — when the state itself buys or sells (e.g., a state-owned cement plant favoring residents, or a state university charging lower in-state tuition), it may favor its own citizens because it acts as a participant, not a regulator.
- Congressional consent — Congress may authorize state laws that would otherwise violate the Dormant Commerce Clause, because the commerce power is Congress's to share.
Note also that subsidies to local businesses funded from general revenue are generally permissible, whereas discriminatory taxes are not.
A state enacts a law forbidding the sale of milk in the state unless it was processed at an in-state facility, citing local job preservation. An out-of-state dairy challenges the law. What is the most likely result?
Article IV Privileges and Immunities versus the Fourteenth Amendment
Two different 'Privileges and Immunities' clauses are constantly confused on the bar.
The Article IV Privileges and Immunities Clause (the 'Comity Clause') bars a state from discriminating against citizens of other states with respect to fundamental rights — chiefly the right to pursue a livelihood (employment) and access to courts. Discrimination is permitted only if the state has a substantial justification and no less-restrictive means; the out-of-staters must be a peculiar source of the evil.
Critically, this clause does not protect corporations or aliens (only natural-person U.S. citizens), and it requires intentional discrimination against nonresidents. Toomer v. Witsell (higher commercial shrimping fees for nonresidents) illustrates a violation.
The Fourteenth Amendment Privileges or Immunities Clause is much narrower and protects only the rights of national citizenship (interstate travel, voting in federal elections, petitioning Congress). It is rarely a winning argument — Saenz v. Roe (durational residency requirement penalizing the right to travel) is the modern exception.
Overlap with the Dormant Commerce Clause. A state law discriminating against nonresident economic activity may violate both the Dormant Commerce Clause and Article IV. But note the divergent exceptions: the market-participant exception defeats a Dormant Commerce Clause claim but does not apply to an Article IV claim. So when a state acts as a market participant and discriminates against out-of-staters' livelihood, the Article IV clause may still provide relief where the Commerce Clause does not.
A city requires that all employees on city-funded construction projects be city residents. An out-of-state worker challenges the ordinance. Which doctrine offers the strongest claim, given the city is spending its own funds?
Intergovernmental Immunity and Putting It Together
The Supremacy Clause also yields intergovernmental immunity: states may not directly regulate or tax the federal government or discriminate against the federal government and those it deals with (McCulloch v. Maryland — a state cannot tax the Bank of the United States). The federal government and its instrumentalities are immune from state taxes and regulations that discriminate against them or substantially interfere with federal functions. Conversely, the federal government has broad power to tax and regulate states under nondiscriminatory laws.
On essays, sequence the federalism analysis carefully: (1) Is there a valid federal law? If so, run preemption. (2) If the challenge is to a state law and Congress is silent, run the Dormant Commerce Clause (discrimination first, then Pike). (3) Check the market-participant and congressional-consent exceptions. (4) Separately analyze Article IV Privileges and Immunities for discrimination against out-of-state citizens' fundamental rights, remembering that corporations and aliens are excluded and that the market-participant exception is unavailable there.
Keeping the two Privileges and Immunities clauses and their exceptions straight is the single most common federalism error on the exam.