Super PACs / "independent expenditures" are probably a big part of it. Revolving doors are probably another important mechanism (which allows to bribe people as

Super PACs / "independent expenditures" are probably a big part of it. Revolving doors are probably another important mechanism (which allows to bribe people as long as the payment is delayed until after the bribe-receiver quits their job). Another mechanism that may be important is bribing people by paying their family members (hiring them as lobbyists, investing in their companies etc.).