In a "60 Minutes" interview, former Vice President Joe Biden spoke to "CBS Evening News" anchor Norah O'Donnell about the tightening Democratic presidential race.

O'Donnell asked him, "Do you still consider yourself the frontrunner?"

"I know I'm the frontrunner. Find me a national poll with a notable – a couple exceptions. The last four that have come out – but look, this is a marathon," Biden said. "This is a marathon."

O'Donnell pointed out the last campaign finance filing. "You have less than $9 million in the bank. Bernie Sanders has $30 – nearly $34 million in the bank. Sen. Warren has $26 million. How do you compete against that?" she asked.

"I just flat beat them," Biden said with a laugh. He added, "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."

In a Quinnipiac poll released Thursday, Massachusetts Sen. Elizabeth Warren was leading the race among Democratic voters and independent voters who lean Democratic, with 28% to Biden's 21%. But a CNN poll released Wednesday showed Biden clocking in at 34%, compared to Warren at 19%.

Watch O'Donnell's full report this Sunday, Oct. 27 on "60 Minutes" at 7:30 p.m. ET and 7 p.m. PT on CBS.