Running as something of a patrician populist, Mr. Steyer brushed aside the dissonance of someone with his résumé — Exeter, Yale, Stanford, Morgan Stanley, Goldman Sachs — paying for ads that castigate the influence of “the powerful and well-connected.”

“I am the outsider in this race,” Mr. Steyer said in an interview. He described Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont as “part of the establishment” and asked whether the front-runner in the polls, former Vice President Joseph R. Biden Jr., really understood what this moment called for .

“The question really is for anybody running, including Vice President Biden, are you aware of how much has to change?” Mr. Steyer said, outlining a two-pronged agenda that would begin with rule changes to curb corporate power followed by significant action to address climate change. He has spent more than $7 million on television so far, according to ad trackers, concentrated in the early voting states of Iowa, New Hampshire, South Carolina and Nevada.

He has paid up to $10,000 for one 30-second broadcast spot in Boston, even though the New Hampshire voters he is targeting are a small fraction of the audience. No target audience appears too small. In Iowa, he is saturating viewers of Black Entertainment Television in Cedar Rapids seven day a week with spots as cheap as $11.

His rivals have accused him of simply buying his way in. “The Democratic primary should not be decided by billionaires,” Ms. Warren said on Twitter the day Mr. Steyer entered the race.

Activists and Democratic officials have generally been muted in their criticism of a top party financier who has spent hundreds of millions of dollars in the past decade. Many privately acknowledged having received Mr. Steyer’s funds in the past and said hopes for his money in the future had kept them silent.

Amanda Litman , the executive director of Run for Something , which encourages Democrats to pursue local office, said that Mr. Steyer could spend his money however he wished but that it would “go a lot further toward making progress on his goals if he invested in state legislatures.”