Barack Obama's presidency marks our democracy's triumph over half the problem of race in America. It underscores the vitality of America's most distinctive and powerful master trend--assimilation, an invincible force that selects from, absorbs and integrates difference, not always kindly, but always to the profit of the nation's mainstream. But Obama's win also highlights the stark paradox that is the other half of our racial problem: while black Americans have been fully incorporated into the nation's public life, they continue to be cut off from the private life of other Americans, a separation that accounts in good measure for blacks' besetting socioeconomic problems.

How did we arrive at this strange racial pass? Blacks have always figured in a complex way into the progress of American democracy. Slavery, under which they suffered for nearly two thirds of their history in America, was a brutal form of double exclusion: from both the public sphere and from the private, intimate sphere of the dominant group. The slave was the quintessential outsider: he was not, and could not be, a citizen participating in the public sphere, nor could he belong to the community, family or formal culture of the master class.

Ironically, this double exclusion facilitated the growth of democracy in America as well as the assimilation of its white immigrants. Democracy emerged first--not accidentally--in the colonial slave South precisely because slavery encouraged a deep bond of racial solidarity among all classes of whites: we-the-people, white and free, were contrasted to the outsiders, domestic enemies, black and unfree. The black presence gave value to whiteness, a positional good eagerly embraced by immigrants who poured into the new nation during the 19th century. However little these newcomers had in common when they were in Europe, on these shores they discovered that they shared one precious thing--their whiteness, which is to say, their non-blackness, and the absence of the stain of slavery. That helped to forge a new identity and a vital bond in the great and growing republic.

Abolition merely freed individual slaves from their masters. It did not abolish the culture of slavery, with its emphasis on the public and private exclusion of blacks. To the contrary, the Jim Crow system that replaced slavery legally reinforced and institutionalized the double exclusion of ex-slaves and their descendants.

The 20th-century political struggles of blacks that culminated in the civil-rights revolution marked the second great chapter in the liberation and incorporation of black Americans. Its achievements were extraordinary: in less than a generation the entire institutional fabric of Jim Crow was dismantled; blacks achieved legal equality and access to the nation's educational and political system. White racial attitudes underwent a profound change, not only in the rejection of notions of racial inferiority by the great majority, but in the acknowledgment of blacks as an integral part of the nation's body politic. The rise of a black middle class, the integration of the military and the remarkable role of blacks in the nation's cultural life--areas of which they came to dominate--were all part of this process. Nowhere was it more pronounced, however, than in the rapid ascent of blacks at all levels of American political life. Obama's presidency is the denouement of this astonishing process of mass democratic inclusion. Blacks are now clearly an integral part of America's public sphere.

But if the work of political inclusion is largely done, that of social incorporation is half finished and may be regressing. While blacks have made absolute gains in income and education since the 1960s, their relative position has not changed and, after the Bush years, threatens to worsen. The black middle class has a fragile hold on its status. Its median household income declined to $30,945 between 2003 and 2005, a mere 62 percent of the white median. In 2002 the median net worth of white Americans ($88,000) was 14.5 times that of blacks, whose net worth (the total value of all their assets, less all their debts and liabilities) was a paltry $6,000. The fragility of their status is reflected in extraordinarily high rates of downward mobility: half of all blacks born to middle-class parents are downwardly mobile; more than half of them fall to the very bottom of the income ladder. The black poverty rate rose from 21.2 percent in 2000 to 24.5 percent last year, and the bottom fifth of the black population is worse off relative to poor whites than at any time over the past three decades.

In the private sphere, blacks remain almost completely apart from whites. Indeed, they are more separate now, in most areas of the country, than at the end of the '60s. And segregation is worse in those parts of the country that have the highest levels of black participation in public life. New York, the liberal heartland of America, in a state where a black man is governor, has among the worst levels of segregation in the nation. So does Chicago, the city that gave Massachusetts its current black governor and that gave the nation its first black president.

Racial preferences and ethnocultural differences are obviously part of the explanation. During the early phase of the civil-rights movement, black leaders such as Martin Luther King Jr. strongly advocated integration in both the public and private spheres, believing, correctly, that separation always entails inequality. But a later generation of black leaders, partly in reaction to the white backlash at black progress, partly out of black pride and a growing black-identity movement, actively promoted apartness in personal life. Most black leaders now accept school segregation, as long as blacks get an equal share of educational resources. Separate but truly equal in private life is increasingly the preferred position, though glossed over with multicultural rhetoric.

Whatever the reasons, the persisting separation of blacks in private life is a tragedy for the group, since it cuts them off from vital social networks and the essential cultural capital that comes only from intimate social relations with successful members of the dominant group. Obama's presidency has the potential to change this. His policies should improve the economic condition of all disadvantaged Americans. Beyond this, there are strong hints from his speeches and writings that he will use the bully pulpit of the presidency to encourage blacks to embrace those mainstream cultural values and practices that have served him so well. His own life and spectacular achievements are, after all, a living demonstration of what integration promises: not so much the transcendence of race as the mainstreaming power of cultural fusion and the fulfillment of King's vision of America as a "beloved community" whose "ultimate goal ... is genuine intergroup and interpersonal living."