As leader of a 20,000-member mega church, Warren says some issues are non-negotiable: abortion, gay marriage, stem-cell research, human cloning and euthanasia.
This tempest in the Christian teapot over the invocation has no precedent.
"There used to be a Protestant a Catholic and a Jew," said Thomas Reese, senior fellow at Woodstock Theological Seminary at Georgetown University. "Now we get conservatives and liberals. I think it shows how politicized the religious community has become."
George Washington never had a prayer at his inaugural it was only in 1937 that the invocation became tradition. Franklin Roosevelt asked a Catholic supporter of the New Deal to join a protestant in prayer. Later, President Harry Truman added the first Jewish rabbi; and Dwight Eisenhower invited a Greek Orthodox minister.
Jimmy Carter cut it back to a Protestant and a Catholic. Ronald Reagan had only a Presbyterian at his first inaugural and later added a Catholic and a Jew. George H. W. Bush and Bill Clinton had Billy Graham, with Clinton adding another Baptist in 1997.
Prayer should be as "inclusive as possible," according to Reese. "The minister leading the prayer should not deny any aspect of his faith to please others, but he need not have every aspect of his faith expressed in his prayer."
The evangelist Graham never mentioned Jesus in his inaugural prayers.
By extending an invitation to both Warren and Robinson, Obama is "trying to reach out to all sorts of people and some of them don't like each other," said Reese.
"Warren and Robinson won't find common ground on abortion or gay rights, but Obama can bring them together in concern for the poor or health care or doing something for the victims of AIDS in Africa," he said.
In the two years since Obama has been invoking a message of common ground, a group of disparate voices -- both progressives and evangelicals -- has been shaping a shared agenda on social issues.
The proposal of shared goals -- "Come Let Us Reason Together Governing Agenda" -- is a call to Obama and to Congress to end what it calls the "culture wars."
Spearheaded by the progressive think tank Third Way, it includes religious leaders like the Rev. Joel C. Hunter and Dr. David Gushee, religion scholar Dr. Robert P. Jones and the religious group Faith in Public Life.
The agenda calls for agreement on four central issues: reducing abortions by increasing support for pregnant women and new families and adoption; protecting the rights of gays in the workplace, with an exemption for faith-based employers; renouncing torture; and supporting immigration reform.
"We are looking for principles in common: respect for human dignity, the golden rule, pragmatics and optimism are the common threads of the project," said Rachel Laser, director of Third Way's cultural program.
Asking Warren and Robinson both to share a role in the inauguration, is exactly the kind gesture this country needs, she said.
"Obama is a man of the big tent, letting more people come into the tent of progressive politics, expanding the tent to include someone like Warren and to simultaneously choose someone like the first openly gay bishop," said Laser told ABCNews.com.