David Maraniss, an associate editor of The Post, is the author of “Barack Obama: The Story” and “First in His Class: A Biography of Bill Clinton.” This column is part of an occasional series on the 2012 presidential candidates’ political lives.

On two historic election nights in Chicago, Barack Obama’s face has told the story. Four years ago in Grant Park, the solemnity of his expression after he took the stage revealed a man at last feeling the full weight of expectations. While his supporters cried and laughed and swayed with joy, his countenance reflected the responsibilities he soon would bear as president. On Tuesday, inside McCormick Place, his hair was grayer, his skin more creased, the crowd not so spontaneous. Yet his face betrayed an incredible lightness of being that went beyond the simple relief that he had won reelection.

Second terms often bring a new set of frustrations for a president, following the laws of diminishing returns and lame-duckiness. But history also shows that a second term is required to create, or to ratify, presidential greatness — and in that sense, Obama is not ambivalent about his ambitions. Since he first thought about being president, a notion that came to him relatively late compared with most politicians, he has wanted to be a great one. When he stepped onto the stage Tuesday night, he realized that he has that chance.

Obama’s reelection solidifies his past and opens his future. A defeat after one term would have forever changed the meaning of his being the first African American president. It has been said that in the integration of Major League Baseball, Frank Robinson’s firing as the first black manager was as important a step toward equality as his hiring. With the presidency, however, where the stakes are so much higher and the historical resonance so much deeper, Obama’s defeat would have brought comparisons, fair or not, to the racial backsliding of Reconstruction.

For Obama, race is important but never overriding. As he found his identity as an African American, the particulars of his biography gave him a universal sensibility. He has a sophisticated understanding of race in America but does not define his presidency in those terms. The fact that his reelection affirmed his first-term accomplishments, and especially assured the survival of his health-care initiative, is more important to him than any racial ramifications of victory or defeat.

At various points during his first term, Obama convened evening round tables of historians at the White House. According to several in attendance, the discussions ranged widely, but the central question Obama pursued was what it would take to reach lasting greatness, beyond the color of his skin. These were not as frequent as monthly seminars, but the president talked with these scholars more often than he played golf with members of Congress (three such outings out of 104 presidential rounds on the links, according to Mark Knoller, a veteran reporter and the go-to guy for White House statistics). Since Obama is often criticized for his reluctance to play the political schmoozing game, some would argue that his pursuit of greatness might have been better served hacking around with congressmen than talking with historians, but that is not how this president operates.

Although Obama is traditional and cautious in most respects, he moves to his own unusual rhythms. He has confidence in doing things his own way. At times he appears a bit slow to act, or detached, or overconfident, or unfocused or behind the curve. And then something happens, and all of a sudden he is not behind but ahead, and what seemed foggy becomes clear. He rationally figures out the traps and works around them in his own fashion. The trendy thing now is to give all credit for his reelection to his technologically precise and proficient ground-game-changing campaign team. It certainly worked wonders. But in the end, it always comes back to the nature of the man at the top. If he ran in some respects a disappointingly small campaign, it was in the service of something larger.

Some people never grow or adapt but only become more of what they were, ending up caricatures of themselves. Throughout his life, Obama has shown a capacity to adapt, to learn from his experiences and mistakes and to become something more than he was. I don’t expect him ever to bridge the country’s ideological divides, or to get the people who hate him to stop hating him and realize that what they see as a threatening otherness is actually a quintessential American story. I do not expect that his efforts to find middle ground on the “fiscal cliff” and the federal deficit will satisfy right or left. Nor do I expect him to fully open up to the press; his administration is far too closed and controlling. But I do have a sense that he will keep working his way through problems, rationally, one after another, until his accomplishments leave a lasting mark in history.

Late on election night, after Obama’s victory was clinched, Mark Leibovich of the New York Times, a friend and former Post colleague, came up to me in the press workspace at McCormick Place and asked: Was I at some level proud of what the subject of my latest biography had accomplished? It was not a personal matter, I said. I have absolutely no personal relationship with the president. I did not fly around with him on Air Force One or play basketball with him or ask him to explain the tricks to being president. I just studied his life and tried to figure him out. And in that sense, yes, I felt a sense of pride for him. I could see the uncommon arc of his life, what he had overcome, all of the contradictions he had tried to resolve, what had burned inside him and what he was aiming at — and that he just might get there.

Read more from the Political Lives series:

David Maraniss: Obama’s debates point to his way with words

David Maraniss: The night Obama first shined

David Maraniss: What drives the Obama haters and doubters

David Maraniss: Obama is his mother’s son

David Maraniss: Obama’s military connection

David Maraniss: The polygamists in the Obama and Romney family trees

David Maraniss: The parallel lives of Barack Obama and Bill Clinton

David Maraniss: The luck that propelled Obama’s rise