The campaign also crossed the 165,000 unique donor threshold during its end-of-quarter blitz, meeting the new requirement set by the Democratic National Committee to make the November debate stage. But Mr. Booker is still short one qualifying poll . (He has already qualified for the October debate two weeks from now.)

The campaign did not release its current cash on hand or average donation size on Tuesday, saying it was still calculating those figures.

Mr. Booker’s financial struggles have mirrored his similarly stagnant polling, constantly in the low single digits. But he continues to rack up endorsements in key early states: His 84 endorsements in New Hampshire alone are more than those received by any other Democratic candidate, according to his campaign.

Though every campaign is starting to dig into its war chest as the primary season nears its final winter sprint, Mr. Booker’s campaign has been particularly dependent on a steady flow of cash.