Barack Obama can fix his rhetoric (as he did last night). But can he fix his demographics? He won big in North Carolina and nearly bumped Hillary Clinton off in Indiana. He won the expectations game in a big away. Still, some perspective is in order:

[H]is victory in North Carolina depended heavily on his overwhelming (91%) share of the black vote, which made up about a third of the primary electorate. Mrs. Clinton won 61% of white Democrats in North Carolina, according to the exit polls, and 65% of white Democrats in Indiana. Mrs. Clinton also broke even among independents. Clearly Mr. Obama’s early promise of a transracial, postpartisan coalition has dimmed as the campaign has progressed and voters have learned more about him.

The question remains whether the McCain campaign is determined and nimble enough to snatch those Hillary Clinton voters away and keep Obama boxed in with a narrow base of African Americans, young people, and ultra-liberal voters. What we know is that, given running room, Obama will sprint to the center and expand his appeal to the very voters whom he let slip through his grasp in Ohio and Pennsylvania. And he will do an effective job of arguing that McCain will represent a third Bush term.

McCain’s challenge is both to define his opponent as outside the political mainstream and to avoid being defined as a Bush clone. It will take a clear and concerted effort by the McCain team–more than biography and an appeal to “experience.” Neither got Hillary Clinton very far.