The Presbyterian Church (U.S.A.) is set to change its rules to allow gay ministers Tuesday, marking a milestone for American Protestant churches. The denomination, which already allows female ministers, rejected a similar push just two years ago, but several presbyteries—regional groupings similar to dioceses—have switched their votes, while other large congregations have left the denomination. The Twin Cities presbytery is expected to put the measure over the top Tuesday. The church will join the Episcopal Church, Evangelical Lutheran Church, and United Church of Christ in allowing gay clergy. The vote will affect the church’s approximately 2 million members, but not members of the Presbyterian Church in America, a small and more conservative splinter group.