Honestly starting with the re-overturning of "money is people" also known as Citizens United would be a good start. This act more or less made it so money is considered free speech which allowed any type of Corporation to spend as much as they want on political groups, it was spearheaded as a thing that the country needed to avoid blocking things such as smear campaigning your opponent. But what it actually did was more or less remove the $5,000 limit that packs and super packs had on financing campaigns and and political donations, because all the Super PAC has to do now is say they aren't politically aligned with a party and they can just funnel as much money into that party as they like, which obviously puts any party that remotely goes against profit(in most cases the democratic party because they generally want more social styled programs) at a significant disadvantage

Not to mention the federal committees that were intentionally implemented to stop corruption that happened within the government because we knew that we couldn't be trusted to deal with important things such as communication and Airline Administration are being gutted by the same system that was supposed to protect them. While everyone's using the excuse of well they're not doing anything so why have them. They're not doing anything because they can't, hell the FCC has tried and the court system is saying they don't have the right to rule over the department that they're a committee over. It's ridiculous

There is an opinion that this is what allows corporate and other power to exist legally. Otherwise it'd just all go Al Capone again, not vanish nor diminish.