Exactly this. A lot of US political institutions can be defined by the mechanism of checks and balances that are built into them allowing for critical scrutiny

Exactly this. A lot of US political institutions can be defined by the mechanism of checks and balances that are built into them allowing for critical scrutiny for anyone who cares to look into them. Hell, you can even go and sit in on Supreme Court sessions in DC if you like. So, even up to the top the processes by which decisions are made are accessible and under constant observation. (The phrase 'adversarial observer' is spot on) If something is amiss, it's more likely to be spotted than in many other countries. There's still plenty of corruption and obfuscation happening in US politics but the act of voting and having votes counted is fairly good. Check Gerrymandering out if you want to see how votes can be unfairly counted.