Barack Obama in Candidates and the Pulpit

From the AP:

Heading into the most racially diverse contest yet in the presidential campaign, [Senator Barack] Obama took to the pulpit at Martin Luther King Jr.'s Ebenezer Baptist Church on the eve of the federal holiday celebrating the civil rights hero's birth 79 years ago. His speech was based on King's quote that "Unity is the great need of the hour."

The words he spoke from the pulpit were certainly applause-worthy:

"The divisions, the stereotypes, the scape-goating, the ease with which we blame the plight of ourselves on others, all of that distracts us from the common challenges we face: war and poverty; inequality and injustice," Obama said. "We can no longer afford to build ourselves up by tearing each other down. We can no longer afford to traffic in lies or fear or hate. It is the poison that we must purge from our politics; the wall that we must tear down before the hour grows too late."

But Senator Obama is a candidate for the Presidency of the United States. And this church presumably enjoys the tax-exempt status of most churches. How do we distinguish when someone is speaking from the pulpit as a candidate and when s/he is speaking as a private citizen to celebrate the ideas and achievements of a great man? Is it even possible to do so?

It appears, then, that this church may have committed a no-no:

Section 501(c)(3) of the IRC prohibits organizations that are exempt from federal income tax under its provisions, including Catholic organizations exempt under the USCCB Group Ruling, from participating or intervening in political campaigns on behalf of or in opposition to any candidate for public office. This prohibition has been interpreted as absolute.

That document, entitled "2007 Political Activity Guidelines for Catholic Organizations", is from the website of the United States Conference of Catholic Bishops and presumably applies equally to the Baptist Church at which Senator Obama spoke.

Even hypothetically, suppose this church allowed other candidates to speak from the pulpit? Would that equalize their invitation to Senator Obama? Or would that only exacerbate the problem of mixing politics with a tax-exempt institution?

UPDATE

Senator Hillary Clinton, also a candidate for the Presidency of the United States, visited the Abyssinian Baptist Church in Harlem yesterday where she received the endorsement of its pastor, the Reverend Calvin O. Butts III. Such an action by the good pastor appears to fall well within the above list of prohibited activities.