With all the fuss over who is praying at the Inauguration and how they are praying, I found Saturday's article in the Wall Street Journal: The Power of Prayer by Steven Waldman, a very interesting history of how this tradition evolved.
If you're not up to reading the very lengthy article, here is my brief summary.
Surprisingly to me, this tradition is of recent origin. While the first presidents issued "prayer proclamations" periodically that drew controversy, pray-ers were not included in their inaugural ceremonies. This tradition dates only from 1937.
Although most would agree that America was a less tolerant and diverse nation then, the roster of "prayers" was more diverse than it later became. Truman had a Protestant minister, a Catholic priest and a Jewish rabbi. From 1937 until 1985 (except for the Carter inauguration) inaugural prayers were offered by what Waldman dubbed "the four person prayer scrum." (Love that term!) The prayers given were all explicitly and unabashedly Christian or Jewish.
Ronald Reagan invited just his personal pastor to his first inauguration, but then returned to the four person prayer team at his second inauguration. After that, both Bush 41 and Bill Clinton only invited "America's pastor", Rev. Billy Graham. Bush 43 invited only Franklin Graham (Billy's son) to his first inaguration and then reinvited him and added Rev. KirbyJon Caldwell to the second inauguration.
Barak Obama followed these precedents by inviting only one pastor to pray at his inauguration--Rick Warren. And Rick Warren's prayer was made in the name of Jesus and he closed it with the Lord's Prayer, following the explicitly Christian model of recent history.
It's fascinating that, as Steven Waldman pointed out, the prayers at Presidential inaugurations have become less inclusive as the country grows more diverse. That's not what I would have predicted.