Senator Barack Obama plans to formally announce his candidacy for president Saturday in the capital where he began his political career just 10 years ago. In a video message on his Web site Friday, Obama said he was launching "a journey to take our country back and change the fundamental nature of our politics." "I know a lot of you are cynical about the possibilities of that change," Obama said. "Sometimes it seems as if the game is fixed and it only works for the few and the powerful, but I fundamentally believe there is another brand of politics. "Let's go get to work," he said.