This has been in motion since the late 1970s. Small increments by both parties as GOP tacked hard libertarian right and Dems followed.
Citizen United was a huge step forward but these days there are so many ways dark money can come in - look at our CPC - it is last gen corruption now.
I think democracy's kryptonite was disinformation. Once you had a Fox News and Sinclair widebanding horseshit, horseshit became the new lingua franca for political discourse instead of fact.