Each Senate seat matters.

On March 23, 2010, then-President Barack Obama signed the Affordable Care Act into law. Getting there was a bit of a roller coaster, given the makeup of the Senate at the time. Although Democrats controlled the House by a wide margin in January 2009, the party was still one seat short of the 60-vote threshold necessary to avoid a filibuster. This includes the seat won by former Sen. Al Franken (D-MN), whose victory became official in July 2009, and the two independents, Sens. Bernie Sanders (I-VT) and Joe Lieberman (I-CT), who caucused with the Democrats.