The mainline churches are the “Seven Sisters” of the traditional Protestant establishment:
American Baptist Churches USA,
Christian Church-Disciples of Christ,
The Episcopal Church,
Evangelical Lutheran Church in America,
The Presbyterian Church USA,
United Church of Christ
The United Methodist Church
Those churches were the pillars of establishment Protestantism. However, in the past 50 years they have rejected orthodox Christianity and replaced it with relativistic neo-pagan philosophy with a thin veneer of “Christianity” that questions the divinity of Christ.