Following a decisive win in the Nevada caucuses last weekend, Vermont Sen. Bernie Sanders has begun to build significant momentum in his campaign. 

According to a report by Politico, Sanders came in strong with 46.8%. His leading opponents, former vice president Joe Biden and former South Bend, Ind., Mayor Pete Buttigieg, trailed from a distance with 20.2% and 14.3%, respectively. 

These numbers, however, have not been accepted wholeheartedly by all candidates. In a letter sent to the Nevada State Democratic Party on Sunday, Pete Buttigieg’s campaign alleged a series of irregularities in the Nevada caucus results.

“By most accounts, early voting itself was a success… The process of integrating early votes into the results of the in-person precinct caucuses, however, was plagued with errors and inconsistencies,” Michael Gaffney, access and delegates director, said in the letter. 

Nevada’s hiccup in the primary process is not the first of its kind this election season, falling in just three weeks behind the Iowa caucus meltdown, which left many voters in doubt of the results’ validity. In light of this skepticism, public opinion has begun to reflect that Democrats may be set on a rocky path for uniting over a single nominee. 

Among them is Buttigieg, who has expressed doubt about Sander’s ability to defeat Trump in the general election this fall.

“I believe the best way to defeat Donald Trump and deliver for the American people is to broaden and galvanize the majority that supports us on the critical issues,” Buttigieg said. “Sen. Sanders believes in an inflexible ideological revolution that leaves out most Democrats, not to mention most Americans.”

The next phase in the primary cycle occurs Feb. 29 in South Carolina, where seven leading Democratic candidates will grapple once again for voters’ support. Given Biden’s moderate ideologies and history of strong backing from Southern voters, it is anticipated that he will begin to pick up speed in this weekend’s polls. 

Regardless, polls are estimating a close tie between Sanders and the former vice president. Given Biden’s lagging support thus far, this primary could ultimately make or break his campaign— and just as easily set Sanders towards the title of nominee.