The former first lady countered Obama's Iowa victory with an upset five days later in New Hampshire that set the stage for a campaign marathon as competitive as any in the past generation.

"Over the last week I listened to you, and in the process I found my own voice," she told supporters who had saved her candidacy from an early demise.

In defeat, Obama's aides concluded they had committed a cardinal sin of New Hampshire politics, forsaking small, intimate events in favor of speeches to large audiences inviting them to ratify Iowa's choice.

It was not a mistake they made again — which helped explain Obama's later outings to bowling alleys, backyard basketball courts and American Legion halls in the heartland.

Clinton conceded nothing, memorably knocking back a shot of Crown Royal whiskey at a bar in Indiana, recalling that her grandfather had taught her to use a shotgun, and driving in a pickup to a gas station in South Bend, Ind., to emphasize her support for a summertime suspension of the federal gasoline tax.

As other rivals fell away in winter, Obama and Clinton traded victories on Super Tuesday, the Feb. 5 series of primaries and caucuses across 21 states and American Samoa that once seemed likely to settle the nomination.

But Clinton had a problem that Obama exploited, and he scored a coup she could not answer.

Pressed for cash, the former first lady ran noncompetitive campaigns in several Super Tuesday caucus states, allowing her rival to run up his delegate totals.

At the same time, Sen. Edward M. Kennedy, D-Mass., endorsed the young senator in terms that summoned memories of his slain brothers while seeking to turn the page on the Clinton era.

Merely by surviving Super Tuesday, Obama exceeded expectations. But he did more than survive, emerging with a lead in delegates that he never relinquished, and he proceeded to run off a string of 11 straight victories.

Clinton saved her candidacy once more with primary victories in Ohio and Texas on March 4, beginning a stretch in which she won in six of the next nine states on the calendar, as well as in Puerto Rico.

It was a strong run, providing glimpses of what might have been for the one-time front-runner.