Not long after the first results began rolling in, a super PAC supporting Mr. Buttigieg announced it was buying TV ads in Super Tuesday states. Mr. Biden’s campaign manager declared that “the Biden comeback” had just begun. Senator Amy Klobuchar dropped from her New Hampshire showing yet claimed to have “exceeded expectations.” And Ms. Warren’s campaign manager said her performance at last week’s debate would prove more important than the actual election.

Translation: No one is about to quit this race.

And the longer all the alternative candidates remain, the longer Mr. Sanders can keep carrying states and consolidating his own coalition without a singular rival.

“The Nevada results reinforce the reality that this fragmented field is putting Bernie Sanders on pace to amass an insurmountable delegate lead,” said Kevin Sheekey, the campaign manager for Mr. Bloomberg.

Each has their own arguments for staying.

Mr. Biden, who carried black voters in Nevada, is the best positioned to beat Mr. Sanders in an upcoming state (South Carolina). Mr. Buttigieg has had the strongest showings overall besides Mr. Sanders. Ms. Warren, whose campaign announced a $21 million haul for February, argues she has the money and organization to compete. Mr. Bloomberg has his billions. Ms. Klobuchar’s path — which is taking her to Fargo, N.D., on Sunday — seems less clear and may be more about grabbing spare delegates than the nomination.

The collective impact is clear. A remarkable six candidates all had at least 12 percent of the vote among voters over 45 in Nevada, an almost impossibly even level of fracture.

Joe Biden’s best finish yet is still second place