President Obama is back on the campaign trail. Not literally. But for the first time as president, he is on the stump in the virtual world, heading what political and tech experts say represents Act II of the groundbreaking, tech-savvy political organizing effort that helped take him to the White House. On Monday, Obama hit the keyboard on behalf of his stimulus package, sending e-mails to millions of his supporters through the group called Organizing for America, ( www.mybarackobama.com), a new arm of the Democratic National Committee. The recipients include the army of Americans who signed up for campaign e-mails...