DALY CITY, Calif. -- One of the biggest sources of political donations to Hillary Rodham Clinton is a tiny, lime-green bungalow that lies under the flight path from San Francisco International Airport.

Six members of the Paw family, each listing the house at 41 Shelbourne Ave. as their residence, have donated a combined $45,000 to the Democratic senator from New York since 2005, for her presidential campaign, her Senate re-election last year and her political action committee. In all, the six Paws have donated a total of $200,000...