At $25 million and counting, Gov. Andrew M. Cuomo sits atop the largest tower of campaign contributions of any Democratic politician in America. But this monument to his prodigious fund-raising strength also reveals one of his greatest vulnerabilities, especially if he harbors presidential ambitions.

He has virtually no small donors.

Since the beginning of 2015, Mr. Cuomo has raised over 99 percent of his campaign money from donations larger than $1,000 and nearly 99.9 percent of his funds from donors who gave at least $200, according to an analysis by The New York Times. At one point last year, Mr. Cuomo went six months without reporting a single individual donor who gave less than $200.

“You almost have to try to have that few,” said Michael Whitney, who served as Senator Bernie Sanders’s digital fund-raising manager on his 2016 presidential campaign. He said that if Mr. Cuomo were to run for president and maintain his “comically absent number of small donors,” it could cripple him in an era where both parties, but particularly Democrats, have become reliant on an army of small givers to compete at the national level.

“I don’t understand how he can credibly use his current fund-raising operation and be a viable candidate for 2020,” Mr. Whitney said.