Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE says he's not worried if other presidential candidates have more money than his campaign.

Biden expressed confidence in his campaign, arguing he remains the front-runner despite questions about his ability to raise money — and whether that will weaken his operation as the campaign goes on.

"I know I'm the front-runner," Biden said in a CBS News interview.

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"Find me a national poll with a notable – a couple exceptions," he said, arguing he's been in the lead in most polls. "This is a marathon."

He said he wasn't worried about his fundraising.

"We're on a course to do extremely well. I'm not worried about being able to fund this campaign. I really am not, truly," he said.

Biden raised $15.2 million last quarter and had just $8.9 million on hand.

Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.), in contrast, has nearly $34 million in cash on hand, and Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) has $26 million in cash on hand after the third-quarter. Sanders raised $25 million and Warren raised $24.6 million in the last quarter.

Biden has led the crowded Democratic field in many polls, although Warren has also been at the top of the pack.

The former vice president's average support on polling aggregate site Real Clear Politics is 27.2 percent, Warren's is 21.8 percent and Sanders's is 17.3.