And all four leading Republican candidates for the 2008 nomination have turned down an invitation to a debate on minority issues scheduled to air on PBS this week.

Yet if the marchers at Jena reminded us that America still hasn’t fully purged itself of the poisonous legacy of slavery, it would be wrong to suggest that the nation has made no progress. Racism, though not gone, is greatly diminished: both opinion polls and daily experience suggest that we are truly becoming a more tolerant, open society.

And the cynicism of the “Southern strategy” introduced by Richard Nixon, which delivered decades of political victories to Republicans, is now starting to look like a trap for the G.O.P.

One of the truly remarkable things about the contest for the Republican nomination is the way the contenders have snubbed not just blacks — who, given the G.O.P.’s modern history, probably won’t vote for a Republican in significant numbers no matter what — but Hispanics. In July, all the major contenders refused invitations to address the National Council of La Raza, which Mr. Bush addressed in 2000. Univision, the Spanish-language TV network, had to cancel a debate scheduled for Sept. 16 because only John McCain was willing to come.

If this sounds like a good way to ensure defeat in future elections, that’s because it is: Hispanics are a rapidly growing force in the electorate.

But to get the Republican nomination, a candidate must appeal to the base — and the base consists, in large part, of Southern whites who carry over to immigrants the same racial attitudes that brought them into the Republican fold to begin with. As a result, you have the spectacle of Rudy Giuliani and Mitt Romney, pragmatists on immigration issues when they actually had to govern in diverse states, trying to reinvent themselves as defenders of Fortress America.

And both Hispanics and Asians, another growing force in the electorate, are getting the message. Last year they voted overwhelmingly Democratic, by 69 percent and 62 percent respectively.

In other words, it looks as if the Republican Party is about to start paying a price for its history of exploiting racial antagonism. If that happens, it will be deeply ironic. But it will also be poetic justice.