His activist campaign attracted unprecedented involvement of people online by creating personalized experiences for supporters, allowing them to raise money, meet like-minded neighbors, use phone calls to interact, and get e-mails and SMS updates and calls to action.
Anyone who disputes the idea that his was a true, online grassroots campaign, the first in American history, needs only to consider this statistic. JFK had 21,000 campaign donors; President Obama had 2.3 million.