This growing and seldom-noticed class of political donors — confirmed in recent campaign disclosure reports from presidential candidates — includes thousands of working-class Americans who give in small amounts repeatedly, in some cases compulsively. They defy the common image that the most committed supporters are deep-pocketed high rollers who write checks for $2,500, the maximum, or the bundlers who get rewarded with access and ambassadorships…

The phenomenon is driven by the ease of donating online and the prevalence of e-mail, social networks, blogs and smartphones, which together create the political equivalent of the candy rack beside the cash register.

“With everything else online, there’s a lot of impulse to a donation,” said Peter Daou, a digital media strategist and Internet director for Hillary Rodham Clinton’s 2008 presidential bid. “You’re able to take action on an impulse more quickly, so it’s much more likely that you’ll do it.”