The most striking thing about Barack Obama is not his youth, his oratory, or even the color of his skin. It’s simply that he knows what he’s about. The vast crowd spread out before him in Chicago late on Tuesday night was transported with joy. America and most of the rest of the world hailed the moment as if it were the Second Coming.

But there in the midst of the frenzy, at this moment of supreme accomplishment, stood Obama — cool, collected and already focused not on the historic victory he had just won in defeating the Republican John McCain and becoming America’s first black president, but on the monumental problems he will confront, and that will not await his inauguration on Jan. 20, 2009. This outcome had been predicted (this time, mercifully, the polls were pretty much spot-on). But when the epochal event finally came to pass, it was still hard for most people to come to grips with it. The implications for the foreign and domestic policy of the US, for how America sees itself and how the world sees America, are too vast. The one person who appeared to grasp exactly what had happened, and what it might mean, was... Obama himself.

In two-and-a-half months’ time, he will take the helm of a country embroiled in two draining wars, with its name tarnished around the world, with a slumping economy and bleeding financial system, facing a federal deficit of a mind-boggling $1 trillion. No president since Franklin Roosevelt, three-quarters of a century ago, has faced such challenges.

But as the country’s very foundations have trembled, the one point of calm has been a man of 47, his name all but unknown barely four years ago, and by conventional political yardsticks with next to no experience to speak of. Yet as he spoke Tuesday to America and the world, Obama projected an almost preternatural sense of destiny, as if he had been preparing for the moment all his life. “A new dawn of American leadership is at hand,” he said, and a world long disenchanted with American leadership ached to believe him.

Obama’s mission is now to transform his country. But even before he starts, he has transformed its political geography. The continental divide evident in the two most recent elections is no more. The cleavage between the coasts and the upper Midwest colored Democratic blue; and the heartlands, the West, and the South that remained a uniform Republican red, has been blurred to the point of invisibility.

He is the first Democrat to win more than 50 percent of the national vote since Jimmy Carter in 1976. He has secured the most convincing electoral college victory in a two-candidate contest since the elder Bush’s rout of Michael Dukakis in 1988. Not since Ronald Reagan has a president entered the White House in a stronger position. Obama prevailed in every major demographic group except the over-65s. He may draw on a colossal reservoir of goodwill, even among many of his opponents.

Every victorious presidential candidate says he wants to govern across the political divide: Even the superpolarizing George W. Bush did so in 2000 and 2004. But if anyone means it, Obama does. This election may have swept an African American into the White House, and given Democrats simultaneous control of the White House and Congress for the first time since 1992. But as the president-elect knows full well, the US remains a center-right country. Back in 2004, Obama first made his name with an electrifying speech in which he proclaimed there was not a “blue America” or a “red America”, but a single United States of America. On the printed page, those words read like a cliché. But like most clichés they are true — or at least Americans fervently pray they are true.

Though his mandate for change is sweeping, he is likely to govern from the center. Yes, the US is entering a period of more activist, interventionist government. The economic crisis, the urgent need to improve the nation’s education, health care, and infrastructure, demand no less. Indeed, one of President Obama’s first acts will be the signature of a massive new economic stimulus program (that is, if a lame duck President Bush has not done so already, in the waning weeks of this administration). But it is also a truism of American politics that really important legislation can only pass with bipartisan support, and if ever really important legislation is needed, it is now.

Abroad, the Obama administration must find a way out of Iraq, and prevent the war in Afghanistan, and the situation in neighboring Pakistan, from slipping out of control.

It will be dealing with a resurgent, prickly Russia — which chose Tuesday of all days to announce it was moving missiles to its Baltic region to counter the “threat’” posed by the US missile defense installations in Europe. It must restart work on the stalled Doha round of global trade talks.

At home, the new president not only has to tackle the immediate economic crisis. He must deliver on lavish election promises of middle-class tax cuts and the expansion of health care coverage, even though these can only push the federal deficit still higher. He must build a credible energy policy. He must place the US at the forefront of the battle against global warming. On the campaign trail, the disconnect between the candidates’ economic rhetoric and the grim daily economic reality experienced by voters was often almost surreal. Now Obama has somehow to bring his country down to earth, yet without destroying the enchantment that lifted him to power.

In Grant Park, the president-elect made a start. The changes would come: “We as a people will get there.”

But the journey would be long, and the problems so great that they might not be solved in a year or two years, or even by the end of his first term. Again and again, he wove into his speech his campaign refrain of “Yes, we can”.

But he uttered the phrase less as a triumphant statement of fact than as a quiet aspiration. Henceforth Obama and the Democrats will no longer have the most unpopular president in modern US history to kick around. If they mess up, and on occasion they will, the fault will be theirs alone. But if the overwhelming weight of expectation is Obama’s greatest problem, he by every indication knows how to handle it. Just as during the tough stretches of the campaign, everyone else might lose their heads — but not him.

One way or another, the man about to become the 44th president knows what he’s about.