President Obama is spending his holidays reviewing plans for the new staff he's expected to announce in early January, which advisers say will be "significant" if not "wholesale." Obama's campaign manager, David Plouffe, will replace David Axelrod as the president's top adviser. Gene Sperling and Robert Altman are top contenders to replace Larry Summers as chairman of the National Economic Council. Jim Messina, a deputy White House chief of staff, is heading back to Chicago to start Obama's re-election campaign, creating a vacancy in the upper echelon of presidential advisers. The White House is also hiring an army of lawyers to prepare for oversight investigations from the Republican-controlled House of Representatives. Despite the large-scale shuffle, all of Obama's cabinet members except Defense Secretary Robert Gates are expected to stay on next year.