There are plenty of paradoxes to the effort to keep the bison from getting to Fort Peck. The first is that brucellosis is typically transmitted in the aborted fetus and fluids of an infected cow. Transmission by bulls is unlikely. That means the five bulls sent to Fort Peck as a token of cooperation have spent most of their lives being quarantined at great expense for a disease they don’t spread.

The next shipment of Yellowstone bison tentatively scheduled to go to Fort Peck, possibly later this year, is also all bulls. This is a good way to not build new herds, which may be the point. But Mr. Magnan, fish and game director for the tribal nations, isn’t complaining. He hopes that taking the males through the quarantine process will persuade officials that the reservation can handle the females, too.

Another incongruity has to do with the lack of evidence implicating any bison at all in transmission of brucellosis. In an authoritative 2017 study, scientists traced the genetic lineage of the Brucella bacteria in 27 cattle herds infected around Yellowstone since 1998 and found bison not guilty on all counts. The culprits in every case were elk. There are, however, no plans to contain or cull elk. But unlike bison, elk don’t compete with cattle for grazing rights on public lands.

The Montana state veterinarian, Marty Zaluski, argues that the genetic study means nothing, except that elk interact with cattle more than bison do. “It defies logic to say that Brucella bacteria in bison magically do not affect other animals,” he said, adding that a Brucella infection in a cattle herd in South Dakota in the 1980s was “most likely from bison.” The state has also delayed use of the Fort Peck quarantine facility, he said, because “we don’t have jurisdiction — it’s an independent sovereign nation and not subject to state regulation.” That means the state might have no way to enforce an order for testing or euthanasia.

The Fort Peck tribes have offered to sign an agreement to accept state jurisdiction over quarantined animals, Dr. Zaluski acknowledges. “My concern is all of these agreements are severable, and possession is nine-tenths of law,” he said. “It’s ultimately extremely difficult for me to go into an agreement that potentially jeopardizes Montana’s disease control program when we know those agreements can be severed.”

The notion that Native Americans won’t keep their word is also moderately paradoxical. “Since 1492,” said Mr. Magnan, “Europeans have made promises and reneged on everything, and yet they hang it on us?” He doesn’t bother to add that the 19th-century annihilation of bison was in large part a deliberate campaign to destroy and displace the Plains Indians. Or that restoring bison to the tribes at Fort Peck and elsewhere, after 150 years, ought to be one of the easier acts of reparation for the United States to undertake.

The bison deserve better, too. They are an integral part of the Great Plains landscape they helped create, and their patchy way of grazing is beneficial for water resources, for plant growth and for plant and animal diversity. Keeping them locked up in Yellowstone turns them instead into glorified zoo animals.