The top Democrats fighting for the nomination for president in 2020 grappled Friday with mounting skepticism about their capacity to amass the requisite number of delegates for a primary that could come as early as March.

On Thursday, establishment favorite Sen. Bernie Sanders of Vermont said he wouldn’t run in 2020 despite his intense love for the 2016 Democratic nominating contest. His move highlights the challenge his top challenger, former Vice President Joe Biden, faces as he weighs whether to break with decades of Democratic Party tradition and jump into a contest with little or no lead-up.

The party’s more moderate wing remains deeply skeptical of the senator, whose chance to match the past three candidates that bested him for the nomination -- Hillary Clinton, then Barack Obama, then Sanders -- appear unlikely. Sen. Elizabeth Warren (D-Mass.) has yet to declare her candidacy, and if she does, it will take some time before she can approach Biden's 955 Democratic National Convention delegates or Sanders' 664.

“Some of the other top people who have been in the news are just not people we can count on as really coming out and demonstrating their commitment to run and run with the resources to compete,” said Michael Heller, who advised former President Obama on his 2008 presidential bid.

Heller was speaking at a Brookings Institution luncheon, where Wasserman Schultz, the highest-ranking official to express doubts about a Biden candidacy, told the crowd that “there has been a lot of interest, but a lot of people have expressed interest.” She added that there had been a “lack of coordination” in compiling a committee to draft Biden.

“People are confused about what the various groups really are doing,” she said. “We’ve heard from the Vermont delegation about doing a schedule.”

Wasserman Schultz also wasn’t sure what her potential endorsements in the House are in these early days of the race, saying she has “no idea.”

“That’s probably a better question for that seat,” she said.

The Maryland delegation at the event was overwhelmingly supportive of Biden -- Rep. Donna Edwards, Wasserman Schultz’s district director, choked up as she said he is “the best qualified of all of us.”

Karen Neuman, a former deputy campaign manager for Clinton’s first run in 2008, declined to definitively endorse Biden. “I’m just not ready to declare yet. We don’t know what the long-term plans are for him,” said Neuman, adding, “I think that he has what it takes.”

Michael Boyer, whose daughter is in college and is expecting a second child, said “the Biden line” has a lot of appeal. “I’m just confused by this. He’s the only front-runner from the Democratic Party right now,” he said.

“He’s done it and it worked in 2016. I think he would do it again,” said Jason Kufour, an artist who lives in Pasadena.

News that Biden’s son, former Delaware Attorney General Beau Biden, is battling brain cancer cast a spotlight on the issue, with some supporters questioning whether he could beat cancer in 2020. He lost his first battle with cancer in 2015.

The Democratic cycle, though, appears tailor-made for a would-be nominee to court the party’s wealthier donors who play a large role in securing delegates. The candidates are expected to start raking in donations more than two months before the primary and prepare for grueling campaigns designed to engage grassroots Democrats and reinforce party unity.

When asked to estimate when the presidential nomination fight might begin, Abrams listed her team, saying they’re fully aware that their time is needed to “succeed in a challenging general election.” She said she would “hold our ground” on giving voters more time to read every candidate’s personal story.

“So I don’t think people should be given an answer, at this point, that it’s going to start early,” she said.