The differing approaches between Mr. Sanders and Mr. Carson reflect a wider divide between the two parties. The Democrats, largely through ActBlue and the digital efforts of individual campaigns, have gained a cultural and technological edge in developing a low-cost, quick and seamless online operation — an advantage Republicans admit they largely have been unable to match.
The one exception, at least of late, appears to be Senator Ted Cruz, who raised about half of his total of $12.2 million in the third quarter from donations of $200 or less, most of it — about $4.2 million — through digital platforms. Mr. Cruz has been one of the most successful on the Republican side in building a broad fund-raising base, by bringing in big donations for groups supporting him from a few wealthy individuals while also tapping into grass-roots support networks like Tea Party conservatives and evangelicals.
Other Republicans have struggled to keep up with the Democrats in attracting smaller donors in bulk. Jeb Bush, for instance, managed just $1.4 million in donations of $200 or less — a nickel for every dollar he has raised over all.
This election cycle is something of a departure for Republicans, who were once the party of the small-dollar donor. President George W. Bush built his victories in 2000 and 2004 around small-dollar donors his campaign reached through direct mail. In his first election victory, Republican officials bragged of his support from more than 600,000 donors contributing an average of about only $100 each, far outpacing the Democrats.
But the roles are now reversed, with the Democrats — and Mr. Sanders in particular — capitalizing not only on digital technology, but also on voter demographics and cultural quirks.