SPRINGFIELD, Ill. - Barack Obama (news, bio, voting record) announced his bid for president Saturday, a black man evoking Abraham Lincoln's ability to unite a nation and a Democrat portraying himself as a fresh face capable of leading a new generation. "Let us transform this nation," he told thousands shivering in the cold at the campaign's kickoff. Obama, 45, is the youngest candidate in the Democrats' 2008 primary field dominated by front-runner Sen. Hillary Rodham Clinton and filled with more experienced lawmakers. In an address from the state capital where he began his elective career 10 years ago, the first-term...