The Senate turns to the heart of the battle over curbing gun violence next week when it considers a proposal to expand required federal background checks to gun shows and online firearms sales. In a bipartisan 68-31 vote Thursday, senators rejected an effort by conservatives to block debate on Democrats' gun control legislation. Senators then formally opened debate on the bill, lawmakers' response to the mass shooting in December at an elementary school in Newtown, Conn. Thursday's one-sided vote belied what looks like a difficult path for gun restrictions through Congress. Most Republicans and many moderate Democrats oppose or are wary of curbs they think go too far. Senate Majority Leader Harry Reid says he thinks the debate will last weeks. The Republican-controlled House is waiting for Senate action.