CNN contributor Van Jones claimed Friday that former Vice President Joe Biden could stage a comeback but overall, his campaign had been lackluster for a while.

"He’s not vacuuming in money from the top, he doesn't have a grassroots operation. It just felt like a dead man walking campaign for a long time. But it could come back," he said.

Jones, who briefly served as former President Barack Obama's "green jobs czar," said that Biden's relationship to the former president should be earning him more support.

"The problem is a former vice president, two-term vice president, Obama’s guy, should be just sucking in money. He’s broke. That shows there's a lack of enthusiasm not just at the grassroots level, where he needed that, but also at the top," Jones said.

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"And so it’s very, very hard to understand the rationale in the Biden candidacy as a campaign. He doesn’t have the grassroots enthusiasm. He’s not filling stadiums like Bernie Sanders," he added.

Jones' comments came just before Saturday's primary in South Carolina, where Biden needs to pull out a victory after losing the first three contests in the season.

Meanwhile, Biden has picked up endorsements from some prominent politicians. House Majority Whip Jim Clyburn, D-S.C., and Sen. Tim Kaine, D-Va., who also served as the 2016 vice presidential nominee, threw their weight behind Biden before South Carolina's primary.

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“I’m voting for Joe Biden. South Carolinians should be voting for Joe Biden,” Clyburn said. “I know who he is, I know what he is. I know where this country is. We are at an inflection point.”

Jones was just the latest Obama associate to cast doubt on Biden's candidacy. Early in the race, former White House Chief of Staff David Axelrod questioned the former vice president's "steadiness" and "performance" after changing his stance twice on the Hyde Amendment. He also knocked Biden's "low energy" during January's Democratic debate.

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Austan Goolsbee, a former economic adviser to Obama, joined other former Obama officials in backing former South Bend Mayor Pete Buttigieg for the presidency.

"I love the vice president, I worked with him," he previously told Fox News. "It's not in any way against the vice president and I will support whoever is the nominee against Donald Trump because even the Democratic candidates that are farthest from me in this space -- they're far preferable for my purpose than what the president's doing."

Fox News' Brooke Singman contributed to this report.