Tough call but I am going to go with Citizens United over Shelby vs Holder. Citizens United is one of the three things that broke American politics, along with Mitch McConnell and (insert third thing here, probably Fox News).
Just.. What???
Mitch McConnell broke American politics by abusing the institution of the Senate. Filibusters were not that common before 2009, but today they're routine. The vast majority of the dysfunction in Washington has its roots in McConnell. I'd even go so far as to say that he played a pivotal role in creating Trump.
The Fox News thing wasn't serious, I'm just beholden to the Rule of Three
