In his victory speech in Chicago's Grant Park, President-elect Barack Obama reminded his supporters that he "was never the likeliest candidate for this office". That was true: after all, two years ago the White House odds on a 47-year-old, black, Harvard-educated former university professor seemed improbably long.

But that unusual biography is also a Rosetta stone for understanding the new political coalition Mr Obama wove together to win this remarkable battle. His three most striking personal qualities - his youth, his race and his highly educated affluence - incarnate the three voting groups that made him president.