Now that the federal government has authorized the Mashpee Wampanoag tribe to take more than 300 acres of land in Taunton and Mashpee into trust, the big question is whether the decision will be challenged in court.

Tribal officials say a successful challenge is very unlikely, but all involved are treading very carefully. In its 140-page decision regarding the Mashpee Wampanoag, the Bureau of Indian Affairs devoted 40 pages to whether the agency had the legal authority to take land into trust for the tribe. The bureau concluded it did have the legal authority, but there were a lot of suppositions and interpretations in those 40 pages.

Taking land into trust for tribes has been something of a legal no-man’s land since 2009, when the US Supreme Court rejected a bid by the federal government to take 31 acres of land into trust for the Narragansett Indian Tribe of Rhode Island. The decision threw the federal government’s entire land-in-trust process into chaos.

The Rhode Island case, Carcieri v. Salazar, centered on the definition of Indian. The Indian Reorganization Act permits the federal government to take land into trust for Indians, who were defined in the statute as “all persons of Indian descent who are members of any recognized Indian tribe now under federal jurisdiction, and all persons who are descendants of such members who were, on June 1, 1934, residing within the present boundaries of any Indian reservation.”

The state of Rhode Island argued the key word in the definition was “now” and suggested the only tribes for whom land could be taken into trust were those that currently have federal recognition and were “under federal jurisdiction” in 1934, when the law passed. The Supreme Court agreed with that interpretation, ruling that the federal government improperly took land into trust for the Narragansett because the tribe was under state jurisdiction in 1934.

In the press release accompanying its decision last Friday on the Mashpee Wampanoag, the Bureau of Indian Affairs said it was authorized to take the land into trust under the Indian Reorganization Act “and in keeping with the US Supreme Court’s decision in Carcieri v. Salazar.” More accurately, the bureau dealt with Carcieri largely by ignoring it.

The bureau said there were two definitions of Indian contained in the phrase from the Indian Reorganization Act, the first dealing with a tribe “now under federal jurisdiction” and the second dealing with descendants of tribal members who in 1934 were residing “within the present boundaries of any Indian reservation.”

In a footnote to its decision, the bureau said the comments it received from state and local officials on the Mashpee Wampanoag case focused on the first definition, which was the focus of Carcieri. The bureau, while acknowledging the Mashpee Wampanoag could be viewed as being under state supervision in 1934,  said the comments it received from state and local officials were irrelevant because the agency was basing its decision on the second definition.

The bureau’s decision acknowledged the meaning of the second definition was imprecise, but concluded that the Mashpee Wampanoag did occupy a reservation of sorts in the town of Mashpee that was created by Britain in 1660 and continued in various iterations up through the 1930s and on into the 1960s. The bureau’s decision also held that the Mashpee Wampanoag of today are the descendants of those tribal members from the 1930s.

“The town of Mashpee was specifically established as a protected tract of land for Mashpee Indians,” the bureau’s decision said. “The tribe has a long recorded history at its town and the tribe’s ownership and control over this land, while varying in form and degree over hundreds of years, existed in 1934. Given the extensive historical evidence concerning the town of Mashpee, the sweeping remedial purpose of the Indian Reorganization Act, and the clear directive to interpret statutory ambiguities in favor of the Indians, we find that the tribe had a historic reservation for purposes of the second definition as the term was understood when the IRA was enacted.”

All this matters because the Massachusetts Gaming Commission is facing a big decision on gambling in southeastern Massachusetts. Under an agreement negotiated with former governor Deval Patrick, the Mashpee Wampanoag agreed to pay a 17 percent tax to the state on its gambling revenue as long as the tribe’s casino is the only one in the southeast region. If the Gaming Commission approves another casino license in the area, as a group seeking to build a gambling palace in Brockton wants it to do, the tribe would pay no gambling taxes. The Brockton casino bidder would pay the same 25 percent tax rate as the other casino licensees in Massachusetts.

The big unknown for the state Gaming Commission is whether the Mashpee Wampanoag casino will ever get built. As a point of reference, the litigation surrounding the Narragansett land case went on in one form or another for nearly 20 years.