Bernie Sanders’s commanding Nevada caucus victory has made him a top target for his Democratic rivals.
It is also a growing source of anxiety for establishment Democrats worried that the nomination of a self-avowed democratic socialist could cost the party the White House.
Mr Sanders’s win solidified his front-runner status in the crowded field as the race turns to Saturday’s presidential primary in South Carolina, where his moderate opponents will scramble to try to blunt the Vermont senator’s momentum.
Three days later after that contest, 14 states vote on Super Tuesday, March 3, when one-third of the delegates are awarded.
A strong showing in those states could put Mr Sanders on a smooth path to the nomination against Republican president Donald Trump.
That prospect has amplified concerns for Democrats who believe Mr Sanders’s liberal policies will drive away moderate and independent voters in the general election in November.
Jim Clyburn, the top-ranking black leader in Congress, warned of added risk for Democrats if Mr Sanders was the nominee.
“I think it would be a real burden for us in these states or congressional districts that we have to do well in,” Mr Clyburn told This Week on ABC.
He said that congressional districts that helped Democrats win back the House were moderate and conservative.
“In those districts, it’s going to be tough to hold on to these jobs if you have to make the case for accepting a self-proclaimed democratic socialist,” Mr Clyburn added.
Mr Sanders’s campaign argue the candidate will bring in new voters — largely progressives and young people — who have been alienated by politics.
He successfully relied on that coalition on Saturday to dominate his Democratic rivals in Nevada, pulling far ahead of second-place finisher former vice president Joe Biden and Pete Buttigieg, the former mayor of South Bend, Indiana, who came in third.
Massachusetts senator Elizabeth Warren landed in fourth, while Minnesota senator Amy Klobuchar and Tom Steyer were still in a close race for fifth on Sunday.
“We are bringing our people together,” Mr Sanders said on Saturday.
“In Nevada, we have just brought together a multi-generational, multi-racial coalition which is not only going to win in Nevada, it’s going to sweep this country.”
Mr Sanders’s new status was clear as both Mr Buttigieg and Mr Biden went after him harder than they have before.
In his speech to supporters in Las Vegas, Mr Buttigieg denounced Sanders in his sharpest terms yet, claiming that the senator was calling for an “inflexible, ideological revolution that leaves out most Democrats”.
The stakes were high for Nevada Democrats to avoid a repeat of the chaos in the still-unresolved Iowa caucuses, and it appeared Saturday’s contest was largely successful.
But Mr Buttigieg’s campaign is raising questions about the results, citing more than 200 reports of problems allocating votes.
It wants the state party to disclose more details of the votes and address concerns before releasing final results.
But the party said it was not planning to offer a more detailed voting breakdown and appeared to be inviting the campaign to follow recount rules if it wanted to challenge the results.