For the first time since 1954, the Republican Party controls the White House and both houses of Congress. But the margins are narrow, with control decided by a handful of close races, and the nation faces both economic uncertainty and a possible war. This preview of the congressional session examines the Republican mandate in light of those external factors, profiles the leadership of both parties, and explores what issues are likely to be at the top of the congressional agenda as both Republicans and Democrats point toward the 2004 presidential election.