Bernie Sanders looked to cement his front-runner status in the US Democratic presidential race after his dominant win in Nevada, his rivals sought in rallies on Sunday to blunt his momentum ahead of 15 nominating contests in the next 10 days.

Sanders, an independent Senator from Vermont and self-avowed democratic socialist, rode a wave of support across age, race and ideology to capture 47% of the county convention delegates in the Nevada caucuses, with 88% of precincts reporting.

Sanders’ latest victory is sure to stoke more concern among establishment Democrats who see him as too liberal to defeat Republican President Donald Trump in November. Now they have an additional worry that he may soon be unstoppable in his quest to win the nomination.

But the results in Nevada and the outlook for coming contests are doing little to push the rest of the field to drop out, leaving a cluster of more centrist candidates to divide the anti-Sanders vote and unable to build their own momentum.

Biden, a onetime front-runner in the Democratic race, is hoping to get a boost on Wednesday, when, according to a media report, he will pick up the endorsement of Representative Jim Clyburn, the highest-ranking African American in Congress, who represents a district in South Carolina, a state where voters head to the polls on Saturday in the next Democratic nominating contest.

Buttigieg’s campaign sent a letter, which was seen by Reuters, to the Nevada Democratic Party on Sunday urging it to release data on early voting results, fix errors that might have arisen when counting absentee ballots and explain discrepancies the campaign found before any final tally is announced.