What if the Citizens United case either never happened or the SCOTUS ruled the other way? Would Bernie still run? Would any candidates more, less, or different sources of funding?
Meh. Maybe you'll see big changes maybe not. The big fear was that billionaires could now buy elections. They couldn't get Romney to win in 2012 or none of their preferred candidates like Jeb! in 2016. So Citizens United has yet to effect the White House.
And the same time the GOP has bought both houses of congress and the majority of governors and state legislators. The long term damage is yet unknown