BOSTON—A path to the state’s first tribal casino appears to be clearing faster than expected, but a potential lawsuit from an excluded tribe still threatens to complicate or even delay the process.

 The Mashpee Wampanoag moved swiftly to take advantage of a provision in the state’s new gaming law that gives a leg up to a federally recognized Indian tribe in gaining the sole southeastern Massachusetts casino license. The Cape Cod-based tribe acquired an option on land in Taunton, negotiated a host community agreement with city leaders, and on June 9 received a vote of confidence from residents in a nonbinding referendum.