Obama's challenge

Today, Sen. Barack Obama gives a speech in Philadelphia that will test him and define his candidacy.

If his words live up to the billing of a major address on race, politics and unifying our country, he will have been challenged in a way Hillary Clinton has not. Obama's campaign is coping with incendiary utterances by his pastor at Chicago's Trinity United Church of Christ. The Rev. Jeremiah Wright referred to white America as "the U.S. of KKK A." He also proclaimed "God damn America." Obama sat in the pews for 20 years.

This is a crucible moment for the junior senator from Illinois.

Last week, Obama strongly denounced the words but not the man, and embraced God and country. Experts in communication say he covered crucial points:

"Most importantly, Rev. Wright preached the gospel of Jesus, a gospel on which I base my life," Obama said. "In other words, he has never been my political adviser; he's been my pastor. And the sermons I heard him preach always related to our obligation to love God and one another. ...

"When these statements first came to my attention, it was at the beginning of my presidential campaign. I made it clear at the time that I strongly condemned his comments. But because Rev. Wright was on the verge of retirement, and because of my strong links to the Trinity faith community, where I married my wife and where my daughters were baptized, I did not think it appropriate to leave the church."

Obama claims he did not hear the pastor make inflammatory statements and would have spoken out if he had.

Clearly, with the Pennsylvania primary five weeks away, and Obama's huge challenge among older, ethnic white voters there, that statement won't do it.

Today's speech might. He picked the right backdrop. On Independence Mall, in the City of Brotherly Love, Obama could turn a negative into a positive.

David Domke, professor of communications at the University of Washington and an expert on religion and politics, compares the potential of today's speech to a famous one given by John F. Kennedy in Houston in 1960. "Kennedy had to convince people he was an American who happened to be Catholic," said Domke. "Obama has to convince people he is an American who happens to be black."

With all the heated rhetoric and 24/7 coverage, it will not be easy. Obama is a gifted speaker who has to be more eloquent than usual. His words have to truly unify us.

It's a tall order. If he succeeds, he will have been challenged and tested as never before in his campaign.