As Bush's poll numbers sag, and Sen. Hillary Rodham Clinton's rise, some congressional Republicans are taking a fresh look at former New York Mayor Rudy Giulaini, a social centrist with national recognition in stature.Guiliani earns near-universal admiration among congressional Republicans--an important constituency in the race for the nomination.But even his biggest boosters cannot say for sure whether a big city mayor who supports abortion rights can win over the social conservatives who hold overwhelming sway within the GOP.The key question according to pollster John Zogby is 'How strong will the Christian conservatives be? Will they be able to block Rudy,...