Despite achieving a 60-seat majority in the 111th Senate, Democrats were unable to pass many of their key legislative priorities without support from Republicans. The striking inability of Democrats to govern the Senate despite a filibuster-proof majority demonstrates key differences between the chambers of Congress. Whereas party polarization helps the majority party in the House of Representatives to exert more control over the legislative process, in the Senate it aids the minority. Because Republicans viewed the Senate as their main opportunity for hindering the Democratic agenda, the GOP benefitted from their party’s ideological cohesion and rules favoring obstruction.