The Double Jeopardy Clause in the Fifth Amendment to the United States Constitution prohibits any person from being prosecuted twice for substantially the same crime. The relevant part of the Fifth Amendment states that “nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb.” The Double Jeopardy Clause applies against both state and federal governments. See Benton v. Maryland, 395 U.S. 784 (1969).

But under the “dual-sovereignty doctrine” or “separate sovereigns doctrine” the prohibition on double jeopardy does not prevent dual prosecutions when the prosecutions are conducted by separate sovereigns (governments). For example, if a person engages in criminal conduct that constitutes a crime under both state and federal law—or that constitutes a crime in two different states—the person may be prosecuted by both sovereigns without violating the Double Jeopardy Clause. See Gamble v. United States, 139 S.Ct. 1960 (2019).

The dual-sovereignty doctrine is not an exception to the prohibition on double jeopardy—rather, it follows from the Fifth Amendment's text. The Double Jeopardy Clause protects individuals from being “twice put in jeopardy” “for the same offence.” As originally understood, an “offence” is defined by a law, and each law is defined by a sovereign. Thus, where there are two sovereigns, there are two laws and two “offences.”

In Montana, as in all states, the Double Jeopardy Clause of the Fifth Amendment protects individuals from being prosecuted more than once for the same offense by the same sovereign. This means that a person cannot be tried twice for the same crime within the state's jurisdiction or within the federal jurisdiction. However, under the dual-sovereignty doctrine, as upheld in Gamble v. United States, this protection does not extend across different sovereigns. Therefore, if a person's actions violate both Montana state law and federal law, they may face prosecution by both Montana state courts and federal courts without this constituting double jeopardy. Similarly, if the actions violate the laws of different states, each state may pursue its own prosecution. This is because each government entity (state or federal) is considered a separate sovereign with the authority to enforce its own laws.