Overview

This episode of *99% Invisible* breaks down Article IV of the U.S. Constitution and the 10th Amendment, exploring how these provisions govern relationships between states and between states and the federal government. Hosts Roman Mars and Elizabeth Joh walk through each section of Article IV—from the Full Faith and Credit Clause to the Guarantee Clause—before connecting these principles to the 10th Amendment's anti-commandeering doctrine. The stakes become concrete when California Attorney General Rob Bonta joins to explain how his office has filed 55 lawsuits against the Trump administration in less than a year, using these constitutional provisions as a shield against what he describes as federal overreach. The conversation moves from dry constitutional text to live legal battles over immigration enforcement, federal funding, abortion access, and the militarization of American cities, giving the episode a tense, urgent feel.

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0:00Article IV and the Structure of Federalism

Unlike Articles I, II, and III, which establish the three branches of the federal government, Article IV receives far less attention but is critically important for understanding how states relate to one another and to the national government. Elizabeth Joh introduces a useful distinction: what most people call "federalism" is really *vertical* federalism—the relationship between the federal government and the states. But Article IV also addresses *horizontal* federalism—the relationships among the states themselves.

The first two sections of Article IV deal with these interstate relationships. Section One is the Full Faith and Credit Clause, which requires states to respect the laws, records, and court decisions of other states. Section Two contains the Privileges and Immunities Clause (an anti-discrimination principle preventing states from favoring their own citizens over out-of-staters), the Extradition Clause (requiring states to return fugitives), and the now-defunct Fugitive Slave Clause, which allowed slave owners to reclaim enslaved people who escaped across state lines. Joh notes that this last clause, rendered irrelevant by the 13th Amendment, serves as a reminder of the Constitution's deeply flawed origins and the political compromises that shaped it.

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3:18The Full Faith and Credit Clause: Marriage, DOMA, and the Respect for Marriage Act

The Full Faith and Credit Clause embodies a simple but essential idea: for a federal system to work, states must cooperate with one another. If a court in one state issues a judgment awarding you damages, you can ask a court in another state to enforce that judgment without relitigating the case. As Joh explains, this clause has been "metabolized into our way of being"—most Americans don't think about it because it functions smoothly in the background.

But the clause becomes controversial when applied to marriage. Before the Supreme Court's 2015 decision in *Obergefell v. Hodges*, which recognized a constitutional right to same-sex marriage, states were divided. Some recognized same-sex marriages; others passed laws or constitutional amendments defining marriage as between a man and a woman. The question of whether a same-sex couple lawfully married in one state could have that marriage recognized in another was legally unclear. The Full Faith and Credit Clause didn't provide a clear answer because marriage isn't technically a "judgment" (no court declares you married), and courts had historically allowed a "public policy exception" to the clause.

In 1996, Congress passed the Defense of Marriage Act (DOMA), which explicitly allowed states to refuse to recognize same-sex marriages from other states. Congress could do this because the Full Faith and Credit Clause contains an "effects clause" giving Congress the power to prescribe how states must treat each other's records and proceedings. DOMA used this same constitutional authority to permit non-recognition. After *Obergefell* made same-sex marriage a constitutional right nationwide, DOMA became invalid. But in 2022, after Justice Clarence Thomas suggested in his *Dobbs* concurrence that the Court should reconsider *Obergefell*, Congress passed the Respect for Marriage Act (RFMA). RFMA repeals DOMA and requires all states to give full faith and credit to same-sex marriages lawfully performed in any state—though it does not require states to *license* such marriages themselves. If the Supreme Court ever overturns *Obergefell*, RFMA would become the legal battleground, and the question would be whether Congress actually has the constitutional authority to mandate recognition under the effects clause.

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13:53Section 3: Admissions, Territories, and the Property Clause

Section 3 of Article IV has two parts. The first is the Admissions Clause, which governs how new states join the Union. Congress can admit new states, but no new state can be formed from the territory of an existing state without that state's consent (as happened when Kentucky split from Virginia in 1792). The Supreme Court has also read into this clause an "equal footing doctrine"—new states must be admitted on equal terms with existing ones, not as second-class members.

The second part is the Property Clause, which gives Congress broad authority over federal lands and territories. This clause has been used to impose conditions on territories seeking statehood. Joh gives the example of Utah: Congress required the state to ban polygamy as a condition of admission, and Utah's own constitution still prohibits polygamy unless both the state and Congress agree to change it. This shows that while the Constitution contemplates expansion, Congress has significant leverage over the terms of admission.

Roman Mars notes that the Constitution is essentially "expansionist"—there is no limit on how many states can join. This sits somewhat uneasily with America's self-image as a non-colonial power, but the structure is clearly designed for growth. Joh points to Puerto Rico as a territory that has remained in limbo for decades, with statehood stalled by political calculations about which party it would benefit.

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27:51The Guarantee Clause and the Protection Clause

Section 4 of Article IV contains two provisions that have become surprisingly relevant in recent years. The Guarantee Clause says the United States "shall guarantee to every state in this union a republican form of government." What this actually means is hard to pin down because courts have largely treated it as a "political question"—something for the political branches to resolve, not the judiciary. At minimum, it prevents states from becoming monarchies or dictatorships. But Joh raises a harder question: how far could a state go in restricting voting rights before it ceases to be a "republican" form of government? The founders were comfortable limiting the franchise to property-owning white men, so the clause provides no clear floor.

The Protection Clause requires the federal government to protect states from invasion and, upon request, from domestic violence. This clause has been invoked in two politically charged contexts. In 2023, Texas installed a 1,000-foot line of buoys in the Rio Grande River to deter border crossings, with Governor Abbott citing Article IV's protection clause as justification—arguing that the federal government had failed to protect Texas from an "invasion." The Biden administration sued Texas but avoided the constitutional argument entirely, instead claiming Texas violated federal laws about navigable waters. The case remains pending, and Joh notes that both sides likely wanted to avoid a Supreme Court ruling on what constitutes an "invasion."

More recently, President Trump issued a January 2025 proclamation called "Guaranteeing the States Protection Against Invasion," which suspended the entry of certain aliens and cited Article IV's protection clause as justification. Joh explains that courts are generally reluctant to second-guess presidential determinations in foreign policy and national security, making this a difficult area for judicial resolution. The term "invasion" has become a politically charged metaphor, and both sides are wary of having the Supreme Court define it definitively.

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35:16The 10th Amendment and the Anti-Commandeering Doctrine

The 10th Amendment states that powers not delegated to the federal government nor prohibited to the states are "reserved to the states respectively, or to the people." On its face, this seems like a truism—it doesn't grant any specific powers. But since the 1990s, the Supreme Court has interpreted the 10th Amendment as embodying a broader principle of federalism that imposes real limits on federal power.

The most important of these limits is the "anti-commandeering doctrine." The federal government cannot "commandeer" or order states to enact federal regulatory programs, nor can it force state officials to enforce federal laws. As Joh explains, Congress can regulate private actors and individuals directly, but it cannot treat state governments as its servants. This principle applies even if states *want* to be commandeered—the Supreme Court has said federalism is so important that states cannot consent to having their sovereignty violated.

The anti-commandeering principle also extends to Congress's spending power. The federal government can offer states financial incentives to adopt certain policies, but if the incentive is so large that states have no real choice but to comply, it becomes "coercive" and unconstitutional. This was the basis for the Supreme Court's 2012 decision striking down the Affordable Care Act's Medicaid expansion provision—states that refused to expand Medicaid would lose *all* their existing Medicaid funding, which the Court called "a gun to the head." The phrase "gun to the head" has become a standard reference point in federalism cases.

Joh also introduces the "equal sovereignty doctrine," another judicially created principle not found in the 10th Amendment's text. This doctrine holds that Congress cannot treat states unequally without an extremely good reason. It was the basis for the Supreme Court's 2013 decision in *Shelby County v. Holder*, which struck down the Voting Rights Act's formula for identifying jurisdictions with a history of racial discrimination that required federal preclearance before changing voting laws. Joh predicts that Democratic-led states will increasingly invoke this doctrine as the Trump administration targets blue states for enforcement actions while leaving red states alone.

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49:02California Attorney General Rob Bonta: 55 Lawsuits and Counting

The episode's interview segment begins with California Attorney General Rob Bonta describing how his job transformed after Trump took office. Before Trump, Bonta's office focused on traditional state priorities: public safety, fentanyl, human trafficking, hate crimes, consumer protection, and climate action. After Trump's inauguration, the office added an entirely new function: holding the administration accountable when it breaks the law. Bonta frames this in simple terms: "If Trump breaks the law, we sue him. If he doesn't break the law, we don't sue him."

The numbers are striking. California has filed 55 lawsuits in less than 55 weeks—more than one per week—and has won approximately 80% of the time, though many decisions are from lower courts. Bonta claims his office has protected $188 billion in federal funding that Trump "unlawfully tried to withhold" from California, and has secured victories on birthright citizenship, voting rights, and the removal of federalized National Guard troops from California after six months of litigation.

Bonta is careful to distinguish between California's approach and what critics call "obstruction." He rejects the term "sanctuary state" in favor of "pro public safety, pro community trust state," describing California's Values Act (SB 54), passed in 2017. The law directs limited state law enforcement resources toward fighting crime—murder, rape, robbery—rather than civil immigration enforcement, which is the responsibility of federal agencies like ICE. Bonta emphasizes that this is fully within California's 10th Amendment rights: the federal government can enforce immigration law, but it cannot force states to do its job for them. The 9th Circuit has already upheld SB 54, and Bonta insists that being a sanctuary jurisdiction is "nowhere near the line" of obstruction or interference with federal law.

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58:47Federal Coercion, Funding Threats, and the Limits of Federal Power

Bonta addresses the Trump administration's repeated attempts to withhold federal funding from sanctuary jurisdictions. The constitutional framework here is well-established: the federal government can offer incentives to states, but when pressure "turns into compulsion," it violates the 10th Amendment and the spending clause. Bonta cites two key Supreme Court precedents. In *South Dakota v. Dole*, the Court allowed the federal government to withhold 5% of highway funding from states that refused to raise the drinking age to 21—this was a "modest incentive." But in *NFIB v. Sebelius* (the 2012 ACA case), the Court found that threatening to withhold *all* of a state's Medicaid funding was coercive, leaving states with no real choice.

California has already beaten the Trump administration four times on funding-related lawsuits, including cases involving Department of Transportation funding, Department of Homeland Security funding, and Victims of Crime Act (VOCA) funding. Bonta notes that Trump "backed down and threw in the towel" on VOCA funding. He expects the administration to try again, possibly using a February 1 deadline to withhold funding from sanctuary jurisdictions, and says California remains "on very solid constitutional ground."

The conversation turns to the killing of Renee Goode in Minneapolis by ICE agents, and the federal government's subsequent refusal to cooperate with state and local investigations. Bonta calls this "unprecedented and inappropriate," noting that the federal government blocked access to the crime scene and refused to preserve evidence. He cites statements from Vice President JD Vance claiming federal immigration officials enjoy "absolute immunity," and from Deputy Attorney General Todd Blant, who told Bonta and Governor Newsom that investigating federal officials for crimes committed in California is "illegal and futile." Bonta rejects this outright: "If a federal agent commits a crime on California soil against a Californian, can a California law enforcement entity investigate and prosecute? 1,000% yes."

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1:09:51Abortion, Interstate Conflict, and Multi-State Coordination

The interview shifts to the post-*Dobbs* landscape, where states have diverged sharply on abortion access. Texas has banned nearly all abortions, but telemedicine allows doctors in California and New York to prescribe medication abortion to patients in Texas without ever setting foot there. Texas and Louisiana have begun targeting these out-of-state doctors with civil and criminal liability. This raises questions about the Full Faith and Credit Clause: must California respect Texas's legal proceedings against California doctors?

Bonta explains that California has created "guardrails and protections and legal safe havens" for abortion providers. The state has enshrined abortion rights in its constitution, passed laws protecting patients and providers, and prevented out-of-state entities from using subpoenas to obtain information about legal medical procedures performed in California. Bonta argues that California's decisions "deserve full faith and credit and should be honored by other states," and that there is no constitutional problem with California refusing to cooperate with Texas's attempts to reach into California through "long arm civil and criminal liability actions."

Bonta also describes the coordination among Democratic attorneys general, which he calls a "coalition of co-equals." There are currently 24 Democratic AGs (up from 23 after Virginia flipped in the 2024 election). They communicate weekly, meet regularly, and have been planning since before Trump's election. Bonta says they took Trump's campaign promises and Project 2025 seriously, preparing lawsuits in advance so that if certain actions occur, "all we have to do is dot the I's, cross the T's, press, print and file our complaint." He mentions specific preparations for potential invocation of the Insurrection Act, the Comstock Act (which could be used to block mailing of abortion medications), and other "fringe theory approaches to seizing power."

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1:17:56The Insurrection Act and Threats to Election Integrity

Bonta identifies election integrity as his greatest concern for the coming year. He notes that Trump continues to claim he won the 2020 election, recently sent law enforcement into Georgia to investigate baseless conspiracy theories, and has suggested that if he loses the 2026 midterms, the election must have been rigged. Bonta worries about the "dangerous combination" of Trump's election denialism, his willingness to militarize American cities, and his increasing desperation as polls show public opinion turning against him.

Specifically, Bonta fears the possibility of federalized National Guard troops or Marines stationed at or near polling stations, and attempts to use the U.S. Postal Service to interfere with mail-in ballots. He also expresses concern that the administration might invoke the Insurrection Act, which would create an exception to the Posse Comitatus Act (which generally prohibits the military from engaging in civilian law enforcement). Bonta explains that the Insurrection Act requires an actual insurrection—something that "doesn't exist anywhere in the United States of America"—but that the administration wants the power regardless. He quotes the maxim that "emergency powers beget emergencies," noting that figures like Stephen Miller characterize everything as an "invasion" or "rebellion" not because it's true, but because they want the authority that comes with emergency declarations.

Bonta notes that the Supreme Court recently closed the door on Trump's use of 10 U.S.C. § 12406 (the statute he used to federalize the National Guard in Los Angeles, Portland, and Chicago), but warns that the Insurrection Act provides a different path. If invoked, the military could engage in domestic law enforcement without the usual restrictions, and the administration believes this decision is unreviewable by courts. Bonta calls this view "unlawful and unconstitutional" but acknowledges the threat is real.

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Conclusion

This episode matters because it takes abstract constitutional provisions—clauses most Americans have never read—and shows them being fought over in real time. The Full Faith and Credit Clause, the 10th Amendment, the Guarantee Clause, and the Protection Clause are not museum pieces; they are the legal terrain on which battles over immigration, abortion, federal funding, and even the use of military force are being waged. Attorney General Bonta's interview makes clear that these fights are not academic. His office is filing more than one lawsuit per week, winning most of them, and preparing for scenarios that would have seemed unthinkable a few years ago—military occupation of blue cities, mass deportation operations, and the weaponization of 19th-century laws like the Comstock Act. What stays with the listener is the sense that the Constitution's federalism provisions, designed to balance power between the national government and the states, are being stress-tested in ways the founders likely never imagined. The episode leaves you with the uneasy feeling that the next few years will determine whether those provisions are strong enough to hold.

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Key takeaways

• Article IV governs both vertical federalism (states vs. federal government) and horizontal federalism (states vs. each other), with the Full Faith and Credit Clause requiring states to respect each other's laws and court judgments.
• The 10th Amendment's anti-commandeering doctrine prevents the federal government from forcing states to enforce federal laws or enact federal regulatory programs, even if states consent.
• The Supreme Court has held that federal funding conditions become unconstitutional when they are coercive rather than merely incentivizing—the "gun to the head" standard from the 2012 ACA case.
• California Attorney General Rob Bonta's office has filed 55 lawsuits against the Trump administration in less than a year, winning approximately 80% of the time and protecting $188 billion in federal funding.
• The "sanctuary state" debate is fundamentally a 10th Amendment fight: California argues it has the right to focus state resources on crime rather than civil immigration enforcement, and the 9th Circuit has upheld this position.
• The Insurrection Act, if invoked, would create an exception to the Posse Comitatus Act and allow the military to engage in domestic law enforcement—a power Bonta says the administration seeks despite the absence of any actual insurrection.
• The Respect for Marriage Act (2022) uses the Full Faith and Credit Clause's effects clause to require states to recognize same-sex marriages from other states, creating a backup if the Supreme Court ever overturns *Obergefell*.