President-elect Barack Obama asked the nation Wednesday to make a "renewed commitment" to serving their communities, saying his presidency allows a possibility for national unity through active participation, and warning of big crowds and lots of walking on his Inauguration Day. Mr. Obama, who takes the oath of office Tuesday at noon, said Americans can visit the inaugural committee's new online service tool at USAService.org to host events in their neighborhoods. He detailed his plans to join his wife, Michelle Obama, and Vice President-elect Joseph R. Biden Jr. and his wife, Jill Biden, on Martin Luther King Day Monday to...