Supreme Court Approval Rating Dips to 46%
Down 15 percentage points from 2009
IMO, this is the reason.
Citizens United v. Federal Election Commission, 558 U.S. _ (2010), was a landmark decision by the United States Supreme Court holding that the First Amendment protects corporate and union funding of independent political broadcasts in candidate elections. The 5–4 decision originated in a dispute over whether the non-profit corporation Citizens United could air a film critical of Hillary Clinton, and whether the group could advertise the film in broadcast ads featuring Clinton's image, in apparent violation of the 2002 Bipartisan Campaign Reform Act, commonly known as the McCain–Feingold Act.[2]
http://en.wikipedia.org/wiki/Citizens_United_v._Federal_Election_Commission