Grass-roots giving is reshaping campaign fundraising, and Barack Obama has been particularly adept at cultivating it. From his South Texas home, Chuck Barracato watches the news to see how Barack Obama is doing. When Barracato is moved by Obama's message or senses that the Illinois senator could use some help, he digs into his savings and chips in $25 for the candidate's presidential campaign. Barracato's payments, sent by computer click, add up to $700, maybe a little more. It's not a big sum by the standards of political donations, but it's enough to make Barracato part of a movement that...