LOS ANGELES — For almost 15 years, Kinde Durkee has been one of the go-to accountants for Democratic candidates in California. She and her firm kept track of expenditures and contributions and made sure that candidates and party committees’ campaigns complied with California’s tangled election finance laws.

But just after Labor Day, Ms. Durkee was arrested by the F.B.I. on charges of siphoning hundreds of thousands of dollars from the campaign of a State Assembly member from Orange County for her personal use. The F.B.I. found that Ms. Durkee had control over nearly 400 campaign accounts and had been shuffling money between them — and out of them — for years.

The arrest set off a spasm of anxiety among California Democrats, who feared that they might have been victimized in a scandal that many described, with just a tad of exaggeration, as the political accounting equivalent of Bernard Madoff’s Ponzi scheme.

The latest victim — and so far the most prominent — was Senator Dianne Feinstein, who is up for re-election next year; aides said as much as $5.2 million might be lost. Mrs. Feinstein joins a cast that includes members of Congress and the State Legislature, as well as local party committees that relied on Ms. Durkee.