Small Donors Get Creative to Give Over and Over to 2020 Candidates

The trend is fueled by the increasing ease of giving money online.

The February day that Bernie Sanders began his second Democratic presidential campaign, Christine Peloza gave him $27, the amount Mr. Sanders often boasted was the average donation in his first run. Then, she kept giving, in $3 increments, clicking donate up to 20 times a day.

By the end of June, Ms. Peloza, a 34-year-old office manager at an elderly care facility in Illinois, had donated more than 850 times to Mr. Sanders, making her the most frequent...