Should he run, Mr. Steyer would likely face a far more searching examination of his record than he has to date, including his background as a hedge fund manager who invested heavily in fossil fuels. Several populist candidates, including Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont, have consistently signaled that they would respond aggressively to any billionaire who entered the race and sought to finance a candidacy with a personal fortune.
Mr. Steyer could use that vast personal wealth, estimated by Forbes magazine at $1.6 billion, to fund a television advertising campaign beyond the reach of anyone else in the field. His political groups spent more backing Democratic candidates in 2018 than any other individual except former Mayor Michael R. Bloomberg of New York.
Despite those personal funds, Mr. Steyer may struggle to qualify for the Democratic Party’s next round of debates. His name has not been included in qualifying polls and it is highly unlikely he could attract 65,000 donors by July 16, the deadline to do so for the next set of debates July 30 and July 31.
Mr. Swalwell’s brief candidacy illustrated the limits of simply making the debates. Though he qualified for and participated in the first Democratic debates in June, Mr. Swalwell barely registered in the polls, earning 1 percent support just three times.
A member of the House Intelligence and Judiciary Committees, Mr. Swalwell had sought to gain a following by focusing his campaign around gun control and gun safety. His campaign released an eight-part plan focused on the issue in June that included a call for a mandatory nationwide buyback program for assault weapons.
But neither that plan, nor verbal jabs at former Vice President Joseph R. Biden Jr. and Mayor Pete Buttigieg during the June debate, gave him significant traction.
It was not immediately clear what effect, if any, Mr. Swalwell’s departure or Mr. Steyer’s arrival would have on other candidates in what may still be a crowded 24-person field.