“There is going to be a real income inequality,” Steven Rattner, a Wall Street executive and Democratic donor, said of the coming fund-raising results for the second quarter, which covers April through June. “You are going to see a big separation between the rich and the poor.”

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This is an especially important moment for Mr. Biden: He will soon say how much money he has raised since entering the race on April 25 — the first such disclosure of his campaign — and his team knows the reinforcing power of a big haul to cement his status as the Democratic front-runner. The pressure is intense on other candidates to demonstrate momentum among big and small donors alike, with the aim of raising more money in the spring than the winter, when Senator Bernie Sanders of Vermont, Ms. Harris, former Representative Beto O’Rourke of Texas and Mr. Buttigieg took in the most.

Not everyone is chasing Wall Street cash: Two candidates in the top tier of polls, Mr. Sanders and Senator Elizabeth Warren of Massachusetts, have railed against the financial industry and opted against the kind of fancy fund-raisers with catering and $2,800 admission prices that lubricate the donor industry.

Still, in New York, the supply and demand is so strong that there are fund-raisers almost daily from morning until night.

Hamilton E. James, the executive vice chairman of Blackstone and a top fund-raiser, hosted Mr. Buttigieg at his home on Thursday. The short-selling hedge fund manager James Chanos will hold an event for Mr. Biden on Monday. And on Tuesday, Marc Lasry, the hedge fund manager and co-owner of the Milwaukee Bucks, is gathering checks for Ms. Harris. Co-hosts of that event include Blair W. Effron, an investment bank co-founder and an influential Democratic financier, and Ray McGuire, vice chairman of Citigroup.