Democratic Candidates Fear Bernie Sanders Could Become 'Unstoppable' After Super Tuesday, Former White House Adviser Says

With Sen. Bernie Sanders expected to win Saturday's Nevada caucuses, moderate candidates will be nervously eyeing Super Tuesday as their last chance to derail his progressive campaign, a former presidential adviser and political commentator has said.

David Gergen, who was an adviser to former Presidents Richard Nixon, Gerald Ford, Ronald Reagan, and Bill Clinton, spoke to Newsweek ahead of Saturday's caucuses with Sanders enjoying a commanding lead in the polls.

Other campaigns have reportedly already accepted they cannot defeat the 78-year-old in the Silver State. There is then only one more contest—South Carolina—before 14 states and one U.S. territory have their say on March 3.

"He's favored in a number of states on Super Tuesday," Gergen said of Sanders, "and the concern that some of the other candidates have is whether he becomes unstoppable after Super Tuesday."

Assuming Sanders does as well as predicted in Nevada and South Carolina, he could establish an unassailable lead on March 3 when around 33 percent of all available delegates are up for grabs.

Sanders has emerged as the Democratic frontrunner but it is not yet clear which other candidate—if any—will rise to challenge him for the nomination.

Former Vice President Joe Biden, former South Bend Mayor Pete Buttigieg, Sen. Amy Klobuchar and former New York Mayor Mike Bloomberg have all positioned themselves as moderate alternatives to the democratic socialist, though are struggling to break out of the pack.

Biden in particular has struggled, finishing fourth in Iowa and fifth in New Hampshire. Even in his so-called "firewall" state of South Carolina, his lead over Sanders has narrowed in recent weeks.

Biden is polling second in Nevada, according to FiveThirtyEight, at around 15 percent. Gergen said it is "very important for Biden" to secure second place in Nevada.

Super Tuesday will narrow the field, as candidates who are lagging in delegates, momentum and funding drop out of the race.

"This could break in so many different ways on that Tuesday," Gergen said. "If you've got the money it's worth staying in."

Super Tuesday will also be the first time that billionaire Bloomberg will be on the ballot. He performed poorly in this week's Nevada debate, struggling in the face of withering attacks from other candidates and doing little to win over the audience.

"It was not a great debut," Gergen said. His opponents "came at him with a ferocity I have never seen a party debate, especially the Democratic Party."

Bernie Sanders, 2020 election, Super Tuesday, Democrats
Democratic presidential candidate Sen. Bernie Sanders is pictured during the Democratic presidential primary debate at Paris Las Vegas on February 19, 2020 in Las Vegas, Nevada. Mario Tama/Getty Images/Getty