"Maryland Gov. Martin O'Malley, center, shakes hands with Senate President Thomas V. ""Mike"" Miller after <a href='http://www.cnn.com/2012/03/01/us/maryland-same-sex-marriage/index.html'>signing a same-sex marriage bill on March 1, 2012</a>. The law was challenged, but voters approved marriage equality in a November 2012 referendum."