Actually, no, It wasn't Citizens United--that decision did not "open the floodgates to campaign cash' as is so often claimed. Buckley vs Valeo in '76 did that--what CU did was rip the gateposts out of the ground and widen the flood. But it was already almost impossible to get someone in office who was determined to represent the people rather than the special interests. Arguably it was Santa Clara County vs Southern Pacific Railroad in 1886, which set the idea that corporations were persons with the rights of persons, into law.