It was something of a financial lifeboat. Over the previous three months, Mr. Biden had been spending more than he raised, depleting his cash reserves. The extra $100,000 a day helped keep the campaign afloat, officials said.
Kate Bedingfield, a deputy campaign manager for Mr. Biden, said that Mr. Trump's seeking help from Ukraine "made it clear to the whole world which candidate he feared facing most."
"And we capitalized on that in a way that produced real results," she said.
Mr. Biden's average daily haul would never again dip below the six-figure mark.
Still, Mr. Biden mostly plodded along financially the rest of the pre-primary season. He averaged raising $169,059 per day online last October, $136,518 in November, $128,912 in December and $168,6774 in January.
In other words, there was no growth.
At the same time, donations to his rivals ballooned. By late February, Mr. Biden was teetering politically and had spent only the sixth most of the Democratic field.
South Carolina resurrected Biden
Then came South Carolina.
With Mr. Sanders threatening to seize control of the primary, Black voters gave Mr. Biden a decisive victory -- and online money rained down: more than $5 million on Feb. 29 and $5 million the next day. Days later, Mr. Biden swept through Super Tuesday to amass a delegate lead he would never relinquish.
Mr. Biden would raise $25.3 million online over seven days -- more than he had in the previous four months.