Erin Schaff / Reuters

Ask a lawyer to explain “sovereignty” and you’ll hear an elevated discussion of Enlightenment political thought, along with some name-dropping—Hobbes, Montesquieu, Madison. Ask Terance Gamble, and he will have a more concrete answer: 34 months of his life.

On Thursday, the Supreme Court will hear Gamble’s complaint in Gamble v. United States: If the Constitution protects against “double jeopardy,” what allows both the state of Alabama and the U.S. government to convict and imprison him for the very same crime?

In 2008, Gamble was convicted in Alabama state court of second-degree robbery, a felony. Seven years later, an Alabama police officer pulled Gamble’s car over. A search revealed marijuana, a digital scale, and a 9-millimeter pistol. Under both Alabama and federal law, felons are forbidden to possess firearms. He pleaded guilty to state charges and received a one-year sentence. In federal district court, Gamble was sentenced to 46 months, resulting in an additional 34-month term in prison that will end in 2020.

The Fifth Amendment says that no “person [shall] be subject for the same offence to be twice put in jeopardy of life or limb.” At first glance, Gamble’s double sentences seem to violate that rule because the “offences” were the same—possessing the very same gun after the very same state felony conviction. The catch is that under the “separate sovereigns” rule, a defendant can be prosecuted by the feds and a state—or by two different states—for precisely the same crime. And, in Gamble’s case, there were two different sovereigns involved. By breaking Alabama’s “felon-possession” statute, Gamble “offended” the state of Alabama; by breaking the federal statute, he also “offended” the United States.

That’s why the concept of “sovereignty” is important. Double jeopardy is a legacy of the English common law, in which there is one sovereign, the Crown. If royal prosecutors tried a defendant, the sovereign had had its chance. But the creation of the United States involved the pious legal fiction that the individual states are not just subdivisions of the federal government, but “sovereigns” with independent powers of their own. Alabama’s chance to bash Gamble wasn’t the act of the United States, and vice versa.

Legal historians aren’t sure where the “separate sovereigns” rule originated. The full doctrine wasn’t announced until Prohibition, when a Washington State court convicted a group of bootleggers under state laws against making and selling liquor. Federal authorities then indicted them for violating federal prohibition laws. When the defendants objected, the U.S. Supreme Court said that “an act denounced as a crime by both national and state sovereignties is an offense against the peace and dignity of both, and may be punished by each.” The principle was reaffirmed in 1959, and it remains a basic rule of federal criminal jurisdiction.

There has been constant criticism of the rule, however, and in 2016 the Court began to display some interest in limiting it. In Puerto Rico v. Sanchez Valle, two defendants challenged their twin convictions—one under Puerto Rico law, the other under federal law—for selling the same illegal firearm. The Supreme Court held, 7–2, that double jeopardy barred the federal prosecution.

Justice Elena Kagan’s opinion turned on geometry. “If two entities derive their power to punish from wholly independent sources (imagine here a pair of parallel lines), then they may bring successive prosecutions,” she wrote. “Conversely, if those entities draw their power from the same ultimate source (imagine now two lines emerging from a common point, even if later diverging), then they may not.”

Neither states nor Indian tribes received their “sovereignty” from the federal government, she reasoned; they brought it with them into the American republic. Puerto Rico, by contrast, was granted self-government by its colonial overlords. Thus Puerto Rico’s prosecution of the defendants was a federal prosecution; double jeopardy barred a second prosecution under federal statutes.

Justice Stephen Breyer, joined by Justice Sonia Sotomayor (who has written about Puerto Rico and the Constitution), dissented, arguing that Puerto Rico’s self-governmental powers should make it as much a separate sovereign as a state. Justice Ruth Bader Ginsburg, in a concurrence, suggested that the “separate sovereigns” doctrine “warrants attention in a future case in which a defendant faces successive prosecutions by the whole USA.” Making an odd couple indeed, Justice Clarence Thomas joined her.

The Gamble appeal followed soon after, with the briefs by both parties and amici curiae suggesting that many think the Court is ready to scrap the “separate sovereigns” theory. Those briefs dwell largely on theoretical issues such as the “original public meaning” of the Fifth Amendment and the “core principles of federalism.” Very little is said about whether a new rule would further the concrete aims of criminal justice, or how many cases a change would affect.

According to a view popular with judges, the federal-state relationship is a brilliant invention of wise Founders who wished to make it harder for government to impede “liberty.” Obstacles to prosecution, some believe, are features of the system. Others, including groups who seek the protection of the federal sovereign from abuse or neglect by local sovereigns, see those obstacles as bugs.

In its brief, the Thurgood Marshall Civil Rights Center at Howard University School of Law reminds the Court that a change in the “separate sovereigns” rule, if not carefully managed, might end up making federal civil-rights statutes difficult, or even impossible, to enforce. “Although this case does not concern police misconduct or federal civil rights enforcement, a decision to abolish dual sovereignty inevitably will require reexamination of several interrelated double jeopardy issues that impact on federal criminal civil rights enforcement,” the brief argues. It asks the justices to take care that a decision in Gamble “not adversely affect or otherwise foreshadow any particular outcome when the framework of a civil rights ‘exception’ ultimately arises in future litigation.”

The Howard Law School professor Adam Harris Kurland, who authored the brief, has written a book-length study of double jeopardy and federal-state relations. In an interview, he argued that the issue before the Court is not simply the “intent” or “understanding” of the Framers of the Bill of Rights, but the structure of the post–Civil War Constitution, which envisions a federal role in protecting minority rights. Citing the work of the Yale professor Akhil Reed Amar, Kurland noted that the federal government needs, at a minimum, the power to prosecute state officials, such as police, who use legal authority to violate constitutional rights. Beyond that, hate-crime laws and prohibitions on housing discrimination might be affected by an overbroad opinion that overturns the “separate sovereigns” rule, he said. “I would expect that each member of the Court would not just make the decision in the abstract.” There’s little evidence that the present rule is unworkable, he added; an overbroad ruling might “unravel the complex tapestry of more than 150 years of double-jeopardy jurisprudence and stare decisis.”

The National Indigenous Women’s Resource Center is on the same side. In a brief, its lawyers argue that a wholesale rejection of the “separate sovereigns” rule would roll back a hard-won victory in the fight against domestic violence and sexual abuse in Indian country.

A large number of domestic-abuse cases in Indian country involve non-Indian abusers. Until recently, the Supreme Court held that tribal courts could not prosecute these abusers at all; those cases had to be prosecuted by federal prosecutors, who are sometimes overworked or unsympathetic to victims. But in 2013, Congress added language to the Violence Against Women Act to allow tribal-court jurisdiction over these cases. Under the “separate sovereigns” rule, tribal courts can now convict abusers, but cannot sentence them to more than three years in prison. U.S. attorneys can also choose to prosecute the most egregious offenders and ask for stronger punishment. A broadly written opinion doing away with the “separate sovereigns” rule would wipe out this hard-won progress, the brief warns. It argues:

This Court should preserve the “separate sovereigns” doctrine as applied to prosecutions by both tribal governments and the federal government, either by rejecting Petitioner’s arguments in their entirety or by making it clear that this Court’s decision in this case should not be read as addressing the unique considerations presented in the context of dual federal and tribal prosecutions. This is both the correct application of this Court’s longstanding precedents concerning the pre-constitutional and inherent sovereignty of Tribal Nations, as well as a practical necessity given the sentencing and jurisdictional limitations now imposed on the authority of Tribal Nations.

Mary Kathryn Nagle, the counsel of record on the brief, told me that if the Court does alter the “separate sovereigns” rule, it should note that tribes’ authority has a different, and older, source than that of states. The Court, she said, should take care to ensure that “no lower court mistakenly extends the holding to tribal-court convictions.” Otherwise, she said, the result could “have very negative consequences for the safety of Native women.”

These possible repercussions are important to consider, but in other regards, Gamble is less consequential than it may seem. Unless the Court goes much further than most people imagine, a victory for Gamble will not completely bar dual prosecutions for the same criminal activity, but only for the same specific crime. Federal courts have already evolved what’s called the Blockburger rule to determine when two prosecutions are for the same “offense.” In Blockburger, a defendant challenged two federal convictions for the same sale of illegal drugs—a sale of narcotics not in “the original stamped package,” and a sale of the same drugs “not in pursuance of a written order.” Both were specifically forbidden by statute. The Supreme Court rejected the defendant’s double-jeopardy claim, reasoning that “where the same act or transaction constitutes a violation of two distinct statutory provisions, the test to be applied … is whether each provision requires proof of an additional fact which the other does not.” Numerous state offenses require different facts than similar federal ones; under Blockburger, those cases can proceed.

Some news accounts suggest that a victory for Gamble might imperil Special Counsel Robert Mueller’s investigation of the Trump campaign. The idea is that Donald Trump could pardon his associates facing federal conviction, and that such a pardon would carry over and immunize them from state charges as well. The facts seem to me a good deal less dire. First, about half of the states in the U.S. already bar state prosecutions after federal ones for the same charge; no result in Gamble will change that. Second, many state charges might arise under, say, financial-crimes or fraud statutes that, being different from federal statutes, would pass the Blockburger test. Third, pardons for specific offenses usually follow prosecution. Imagine a scenario in which Mueller charges a Trump confederate with a federal crime. Jeopardy would not apply until that case came to trial; if Trump has to wait for a verdict, time might run out on his term in office before he could issue a pardon. And the Court would have to go completely off the rails to create a new double-jeopardy rule that would allow a president to pardon a defendant in advance of a federal trial and also block state charges in advance.

Terance Gamble’s case is so straightforward that neither side wastes any time discussing it. But appellate courts would do well to be aware that easy cases sometimes make bad law.

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