Sanders won on the strength of his leads in New Hampshire's largest cities. He led his chief rivals in Manchester by more than 2,000 votes and in Concord and Nashua by 500 votes each. Buttigieg performed best in communities south of Manchester, in Boston sleeper suburbs and in college towns such as Hanover, home of Dartmouth College.

Biden, once the national front-runner, has now finished an embarrassing fourth in Iowa and fifth in New Hampshire. Warren, the neighboring state's senator who claimed almost a third of the Democratic vote in an October poll , edged Biden out by less than a percentage point for fourth place.

The two candidates — who between them led 20 of the 39 polls of New Hampshire primary voters conducted before the Iowa caucuses — now face a grueling 11-day slog to the next contest in Nevada and an 18-day wait for the South Carolina primary. Both will have to convince donors and supporters they can regroup and rebuild their campaigns to score a win.

There were troubling signs for both Biden and Warren in Tuesday's outcome.

Warren, who famously has a plan for everything, is getting beat among those who value plans over electability. Among the 33 percent of voters who said they preferred a candidate who agreed with them on major issues, more than a third chose Sanders, and only a tiny fraction chose Warren. Among the three in five voters who said they supported replacing America's health care system with a single-payer plan, three times as many chose Sanders over Warren.

Both Biden and Warren took steps Tuesday to distance themselves from the New Hampshire results, even before the polls closed.

Warren stayed in New Hampshire to concede, offering kind words to Klobuchar and pledging to fight on. In a memo to supporters, Warren campaign manager Roger Lau wrote that Warren's candidate remains "the consensus choice of the widest coalition of Democrats in every corner of the country." He said Warren's formidable campaign organization was poised to win delegates across most of the states and districts that will vote on Super Tuesday,and that her ceiling is higher than Biden's, Sanders's or Buttigieg's.

Each campaign will now have to convince its chief supporters that its candidate still has a path to the 1,990 delegates necessary to win the convention. Without the support necessary to sustain mushrooming national field organizations and seven-figure television budgets, any candidate's campaign withers and dies; when a candidate loses or falls short of expectations, those money problems mount even more rapidly.

But after two early contests in which Sanders demonstrated his years of organizing and Buttigieg overperformed in his final poll numbers, both Biden and Warren face serious challenges.

Warren, too, faces the challenge of breaking through for the first time. She does not lead in polls in Nevada, South Carolina or most Super Tuesday states — the last poll she led was an October WBUR-MassInc survey of her home state's voters — and it is unclear where she will score her first win.

"The road to the Democratic nomination is not paved with statewide winner-take-all victories. This is not a race for governor, the U.S. Senate or the state treasurer's office," Lau wrote in his memo. "This is a district-by-district contest for pledged delegates awarded proportionally."