Why did Scott Brown’s election to the Senate make passage of the Affordable Care Act more difficult?

Scott Brown’s election to the U.S. Senate in January 2010 made the passage of the Patient Protection and Affordable Care Act significantly more difficult because it deprived the Democratic Party of its 60-vote, filibuster-proof majority in the Senate.12

Prior to this special election in Massachusetts, which filled the seat previously held by Ted Kennedy, Democrats relied on that majority to advance their legislative agenda. Because Brown had campaigned actively against the health care bill, his victory left the legislation’s prospects for final passage uncertain and forced Democratic leadership to pursue alternative legislative maneuvers to secure its enactment.12