From the very beginning, the premise and the promise of Barack Obama’s campaign was that it would transcend race. And last autumn the Obama team also knew this was the only way it could win.

The Clinton brand among black voters was so strong, so unbreakable, so resilient a force that even the first credible black candidate for the presidency remained stuck 20-30% behind Hillary Clinton among African-American voters. She was, after all, the wife of the “first black president”, as the author Toni Morrison called Bill.

She had almost all the black political establishment behind her. Her husband, from his days in Arkansas during the civil rights movement, had forged a deep, durable bond with black America. And Obama’s only hope as a young insurgent was in winning a surprise victory in Iowa or New Hampshire, where black votes were close to nonexistent.

A biracial man reared by one white mother and two white grandparents knew that his ability to touch and inspire white voters was his greatest strength. Especially among younger voters, it was critical. And this appeal wasn’t geared only to white audiences. I will not forget a rally over a year ago, filled with predominantly black donors and activists, when Obama recounted how a supporter greeted him at the anniversary of Martin Luther King’s march on Selma.

“That was a great celebration of African-American history,” the supporter said, to which Obama immediately responded: “No, no, no, no, no. That was not a great celebration of African-American history. That was a celebration of American history.” The postracial appeal wasn’t just about necessity. It was also Obama’s core conviction about his own political message.

And after the primaries in Iowa and New Hampshire, where Obama scored extensive white support, the Clintons realised this as well. Flummoxed by this young, charismatic pretender to their dynastic throne, they made a fateful decision: not to compete aggressively for black votes, but to push Obama into the “black candidate” box and leverage white ethnic and Hispanic support instead. And as the Clintons’ losses mounted, the hints became harder and harder to miss.

Before Super Tuesday, Clinton campaign operatives aired rumours that Obama had been a drug dealer – hint, hint – in his younger days. When Obama scored a landslide in South Carolina, Bill Clinton reminded the media that Jesse Jackson had won the state as well. He called Obama a “kid”, perilously close to calling him a “boy”, prompting the former Clinton operative Donna Brazile to say: “I tell you, as an African-American, I find his words and his tone to be very depressing.” The black civil rights icon John Lewis switched from Clinton to Obama. When Clinton told white rural voters that Obama didn’t care about “people like you”, it stung.

In the last months, the Clintons pushed the story about Jeremiah Wright (Obama’s fiery pastor) hard, but the media did all the heavy lifting. The Clintons shrewdly focused their efforts on older, white Democrats in Ohio, Pennsylvania and Indiana (the kind who had once voted for Ronald Reagan) and refused to shoot down categorically rumours that Obama was a closet Muslim, and stopped even addressing predominantly black audiences in North Carolina.

Last Thursday, Senator Clinton – dazed from a brutal setback in last Tuesday’s primaries – went even further. She told USA Today to consult an Associated Press story “that found how Senator Obama’s support among working, hard-working Americans, white Americans, is weakening again, and how whites in both states who had not completed college were supporting me”.

Yes: a candidate was explicitly arguing that she was the candidate of white Americans. No Republican would be so crude, certainly not John McCain. And that became her primary rationale for carrying on. After North Carolina, the short-term electoral costs have evaporated: West Virginia has a black population of just 3.3%, Kentucky has 7.5%, Oregon has 1.9%, Montana and South Dakota both have less than 1%. There are no black superdelegates willing to switch from Obama to Clinton at this point.

And so a strategy that was essentially telling superdelegates that a black man could not win the general election became Hillary’s last resort. In this, the Clintons were egged on by the less principled members of the Republican right.

Black Americans – skilled at judging when they are being dissed – got the message. In last Tuesday’s North Carolina primary, Clinton got only 7% of the black vote – a lower percentage than Nixon or Reagan had won in general elections. If someone had told me last year that a Clinton would get less than 10% of the black vote in a Democratic primary, I would have asked what they were smoking. But in a few months, the Clintons have turned a 30-point lead among African-Americans into a deficit of more than 80 points. No constituency has swung as much over the past few months. And the black turnout last Tuesday was massive.

Obama, mercifully, did not take the bait. Despite the Wright fiasco, he tried mightily not to be racially pigeonholed, as he has his entire life. His victory speech last Tuesday night was full of references to his predominantly white family from Kansas and his love of America.

It was a shrewdly adjusted message. And more interestingly, it seemed to be working – slowly. In Ohio, he won 34% of the white vote; in Pennsylvania, he won 37%; in Indiana, he won 40%. The more the Clintons attempted to polarise the voting racially, the more successful Obama was in deflecting it. His rebuke of Wright probably helped. But also the profound media attention.

The more working-class white voters actually saw and heard of him, the more their fears of the unknown seemed to subside. He won only 27% of white voters without college degrees in Ohio; he won 29% in Pennsylvania and 34% of them in Indiana. And when you look at age, the effect is even more striking. In North Carolina, a southern state, Obama won 57% of white voters under 30 and 45% of white voters under 40.

In the Clintons’ morphing into a crude version of racially angry Reagan Democrats, you can see an almost Shakespearian tragedy. Bill Clinton has a long and admirable record in civil rights; and was on the right side of the struggle in the South in his youth. He has an effortless rapport with black Americans, and they were his core final constituency of support in the darkest days of impeachment.

But like any southerner, Clinton also knew how to navigate racial resentment. In 1992, he interrupted the primary campaign to return to Arkansas to sign the death warrant of a mentally retarded black man. He made a point of attacking the radical black hip hop artist Sister Souljah in his first campaign. He signed off on welfare reform. His genius was in holding together a coalition that included enough Reagan Democrats to win, while never losing wide and deep black support.

But he never ran against a black candidate and neither did his wife. They are used to loving and supporting minorities – as long as the minorities know their place and see the Clintons as the instrument of their salvation. Obama broke that dependency and that relationship. And that was why the Clintons had to do all they could to destroy and belittle and besmirch him.

But in that venture the Clintons are destroying themselves and their legacy and their capacity to bridge the very gaps they now must widen to stay in the race. It is a Clinton tragedy – and one that most Americans seem slowly, cautiously but palpably determined not to make their own.

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