Did Senator Barack Obama's speech in Philadelphia convince people that he is still a viable candidate to be President of the United States, despite the adverse reactions to statements by his pastor, Jeremiah Wright?

The polls and the primaries will answer that question.

The great unasked question for Senator Obama is the question that was asked about President Nixon during the Watergate scandal; What did he know and when did he know it?

Although Senator Obama would now have us believe that he is shocked, shocked, at what Jeremiah Wright said, that he was not in the church when pastor Wright said those things from the pulpit, this still leaves the question of why he disinvited Wright from the event at which he announced his candidacy for the Democratic Party's presidential nomination a year ago.

Either Barack Obama or his staff must have known then that Jeremiah Wright was not someone whom they wanted to expose to the media and to the media scrutiny to which that could lead.

Why not, if it is only now that Senator Obama is learning for the first time, to his surprise, what kinds of things Jeremiah Wright has been saying and doing?

No one had to be in church the day Wright made his inflammatory and obscene remarks to know about them.

The cable news journalists who are playing the tapes of those sermons were not there. The tapes were on sale in the church itself. Obama knew that because he had bought one or more of those tapes.

But even if there were no tapes, and even if Obama never heard from other members of the church what their pastor was saying, he spent 20 years in that church, not just as an ordinary member but also as someone who once donated $20,000 to the church.

There was no way that he didn't know about Jeremiah Wright's anti-American and racist diatribes from the pulpit.

Someone once said that a con man's job is not to convince skeptics but to enable people to continue to believe what they already want to believe.

Accordingly, Obama's Philadelphia speech — a theatrical masterpiece — will probably reassure most Democrats and some other Obama supporters.

They will undoubtedly say that we should now "move on," even though many Democrats have still not yet moved on from George W. Bush's 2000 election victory.

Like the Soviet show trials during their 1930s purges, Obama's speech was not supposed to convince critics but to reassure supporters and fellow-travelers, in order to keep the "useful idiots" useful.

Best-selling author Shelby Steele's recent book on Barack Obama ("A Bound Man") has valuable insights into both the man and the circumstances facing many other blacks — especially those who were never part of the black ghetto culture but who feel a need to identify with it for either personal, political or financial reasons.

Like religious converts who become more Catholic than the Pope, such people often become blacker-than-thou. For whatever reason, Barack Obama chose a black extremist church decades ago — even though there was no shortage of very different churches, both black and white — in Chicago.

Some say that he was trying to earn credibility on the ghetto streets, to facilitate his work as a community activist or for his political career. We may never know why.

But now that Barack Obama is running for a presidential nomination, he is doing so on a radically different basis, as a post-racial candidate uniquely prepared to bring us all together.

Yet the past continues to follow him, despite his attempts to bury it and the mainstream media's attempts to ignore it or apologize for it.

Shelby Steele depicts Barack Obama as a man without real convictions, "an iconic figure who neglected to become himself."

Senator Obama has been at his best as an icon, able with his command of words to meet other people's psychic needs, including a need to dispel white guilt by supporting his candidacy.

But President of the United States, in a time of national danger, under a looming threat of nuclear terrorism? No.

To find out more about Thomas Sowell and read features by other Creators Syndicate columnists and cartoonists, visit the Creators Syndicate web page at www.creators.com. Thomas Sowell is a senior fellow at the Hoover Institution, Stanford University, Stanford, CA 94305. His Web site is www.tsowell.com.

COPYRIGHT 2008 CREATORS SYNDICATE, INC.