President-elect Barack Obama will take office in January with a weapon no president has ever had at his disposal: An online army of more than 10 million supporters who can now be put to use to help carry out a sweeping agenda. The vast lists of e-mail addresses and cell phone numbers compiled by the Obama campaign represent an opportunity for the incoming administration to establish a digital presidency that takes advantage of both new technologies and the wide enthusiasm that greeted Obama's candidacy. In the six days since Election Day, Obama's transition team has taken a series of initial...