New Hampshire Usually Winnows Field. This Year May Be Different.

The police in Exeter shut down entry to her town-hall-style meeting Monday afternoon, directing attendees to an overflow room, as Ms. Klobuchar took the stage and trumpeted her growth in recent New Hampshire polls and her endorsement from several of the state’s newspapers.

“As you’ve probably heard, we’re on a bit of a surge,” she said to applause. Ms. Klobuchar avoided direct criticism of her rivals but dismissed what she called “bumper sticker slogans” like “free college for all,” an obvious reference to the expansive proposals of Mr. Sanders and Senator Elizabeth Warren of Massachusetts.

Even more striking was Mr. Biden’s decision Monday to drop the harshly negative attacks he had aimed at Mr. Buttigieg over the weekend.

After claiming that Mr. Buttigieg had a light resume that could imperil Democrats’ hopes of defeating Mr. Trump, and stating that “this guy’s not a Barack Obama,” Mr. Biden on Monday shifted his attention back to an opponent he’s more at ease attacking: Mr. Trump.

That recalibration may owe to his campaign’s decision to all but throw in the towel on New Hampshire, where Mr. Biden acknowledged in last week’s debate that he would probably “take a hit.” On Monday, his aides announced that Representative Cedric Richmond of Louisiana, a former head of the Congressional Black Caucus, would hold a party in Columbia, S.C., to help counterprogram the New Hampshire results. Mr. Biden held a conference call with South Carolina supporters, and one of his top aides sought to highlight this state’s lack of racial minorities.

“Diverse states are going to have their say before we decide who the nominee is,” Kate Bedingfield, Mr. Biden’s deputy campaign manager, told reporters, alluding to Nevada and South Carolina, which are filled with the sorts of black and Hispanic voters who have long been determinative in Democratic nominating contests.

She is not alone in that expectation.

After decades in which New Hampshire culled the field of top-tier nominees, the top five contenders here are determined to go forward. Financial woes could change those calculations, but, for now, nearly every campaign anticipated a long primary, with a state-by-state battle for delegates lasting well into the spring.

Jeff Weaver, a top adviser to Mr. Sanders, said that as soon as New Hampshire was behind them, they would travel to some of those 15 states casting ballots on March 3.

“You’re going to see, even before Nevada, that he will be visiting Super Tuesday states,” Mr. Weaver said, citing two they had built around Nevada trips: California and Colorado. “Super Tuesday is on,” he added.

First up for Mr. Sanders: North Carolina, where he will hold rallies in Durham and Charlotte on Friday.