Corruption in the US been extensively documented and proven. The revolving door at regulatory bodies, dark money, gerrymandering, no-bid contracts, "kids for cash", the collusion at the DNC before the 2016 primary, unconstitutional domestic spying by the NSA (along with the directer James Clapper lying to congress under oath without consequence), the lies the George W. Bush administration sold the public to justify his wars (and just about everything else surrounding them including profiteering, the use of torture, and many other war crimes), the Whitewater scandal, etc.
You can go back in time as far as you like and you'll find things like The Teapot Dome scandal or The Whiskey Ring.
The kind of corruption we're seeing today is exceptional, but to pretend that anything before now was "isolated incidents" and "unproven theories" is beyond ridiculous. Things right now are bad enough that we don't have to blind ourselves to our own history in order to make it appear worse. It is worse. It doesn't change the reality that corruption has been an ongoing problem in the US and maybe if we'd been more aggressive about punishing it we wouldn't be here today. Sweeping any of it under the rug is the last thing we should be doing.