Democratic presidential candidate Senator Cory Booker (D-NJ) responds to a question during a forum held by gun safety organizations the Giffords group and March For Our Lives in Las Vegas, Nevada, October 2, 2019.

Sen. Cory Booker in the fourth quarter pulled in $6.6 million, a sum that pales in comparison with what other Democratic candidates made, including political newcomer and entrepreneur Andrew Yang.

The amount represents a slight increase from what he raised in the third quarter: about $6 million.

Booker's campaign in an email said more than half of his fourth-quarter total came from first-time donors.

"We're thrilled to have closed out 2019 with our best fundraising quarter yet, despite not being able to join the December debate stage due to the artificial thresholds that prevented viable candidates from participating," said campaign manager Addisu Demissie in an email announcing the funds.

"But to put it bluntly," Demissie said, "we're still behind the fundraising of a field of predominantly white candidates who have been able to haul in significantly greater sums of money or tap into their personal fortunes to fund their campaigns."

Tweet from Booker campaign manager

Booker raked in less than half of what Yang said he raised. The entrepreneur's campaign predicted he'd raised $12.5 million and ended up reporting $16.5 million.

Booker has consistently failed to pick up traction in national polls. He failed to qualify for the December debate, and he has yet to qualify for the debate this month, which is set for Jan. 14 in Iowa.

Sen. Bernie Sanders said he raised more than $34 million, and former Vice President Joe Biden said he raised just under $23 million.

Former South Bend, Indiana, Mayor Pete Buttigieg's campaign said Wednesday that he had raised nearly $25 million in the quarter.

Sen. Amy Klobuchar's campaign said Friday she raised $11 million in the fourth quarter, more than doubling her previous haul.

President Donald Trump's campaign racked up $46 million in donations during the fourth quarter, his campaign said Thursday.

— CNBC's Brian Schwartz contributed to this report.