But the edgier and more negative tone coming from the president’s re-election is highlighting another issue. Successful campaigns tell positive stories even while they are in knife fights, and even as it steps up an effort to define Mr. Romney on its terms, the White House is working to make a positive case for Mr. Obama, one built around themes of fairness and security.

Judging by the difficulties he has had selling his policies and himself for the last three years, going positive in an effective way could prove to be more challenging for Mr. Obama than going negative.

It was almost an article of faith among Democrats following the 2008 election that Mr. Obama would hold an inherent advantage over Republicans in his ability to inspire voters.

Yet the same man who even in the view of his opponents spoke eloquently to the nation’s yearning for a new direction in the last campaign has proved inconsistent after taking office when it came to summoning goose-bump-inspiring magic.