Republican presidential candidate Sen. John McCain, R-Ariz. (Photo by Kimberlee Hewitt)

The battle lines are familiar. They were drawn during the Vietnam War, when McCain was a prisoner of war, and Obama but a child.

Four decades later, the contrast between two presidential candidates has never been starker.

Here is the grizzled former Navy flier who has vowed "I will never surrender in Iraq.'' And there, the brash newcomer with the unlined face whose startling success already is the source of so much lump-in-the-throat pride in the genius of America.

It isn't just a black thing anymore.

Moments before stepping to the podium Tuesday night to acknowledge that he would be the first black candidate nominated by a major party for president of the United States, Barack Obama and his wife, Michelle, knocked knuckles.

It was a tiny gesture so cool, so tight, so loving and so right, that it seemed to encapsulate both the satisfaction of the moment and the new cultural trajectory of American politics.

"Barack and Michelle were giving each other some 'dap,''' says Mark Anthony Neal, a professor of black popular culture at Duke University. "I was watching the speech with my wife and she saw 'the dap' and said, 'Do you see that? A bunch of folks must be wondering what that means.''

WASHINGTON — With just three primaries left in the race for the Democratic presidential nomination, an analysis of results in the 33 primary states for which there are exit polls reveals the decisive role identity politics played in cleaving the party and determining the likely outcome:

Barack Obama's overwhelming margin with black voters trumped Hillary Clinton's broad backing from white women.

The finding suggests that, despite recent attention to Obama's perceived weakness with a segment of white voters because of race, his immediate challenge is to assuage the letdown and even bitterness of some white women who, along with African-Americans, have been the bedrock of the modern Democratic coalition.

Especially for women of Clinton's generation, who fear they may now not live to see a woman president, Obama is less the dashing dreamer and more the arrogant interloper dashing their dream.

WASHINGTON — According to exit polls, Hillary Clinton won 67 percent of the white vote in West Virginia, America's third whitest state. Yet in early March, Barack Obama won 60 percent of the white vote in Vermont, the nation's second-whitest state.

What gives?

America is learning a lot about race this year, most recently that not all white voters are alike. There are enormous regional differences in how whites vote, differences with deep historical roots.