1) Probably mostly the media. Media owners, media leadership, editors, journalists, reporters and so fourth.
On the other hand, it is invalid to not mention money. Money has a major influence, and most of the time when someone is elected, the rich and the corporations, special interests and so fourth are also selecting/electing politicians.
The people are tools, the people are made to believe they rule, and that is the beauty of democracy. It pains to the people the image they want to see, while the reality is different. What better front is there on corruption then the pre-emptive notion that democracy "means that people are in power". While in reality, they are not.
2) The media I would say, but if political scandals they almost have an obligation to report. So in praxis it is the politicias who resign. The people havent thrown a politician out of office in the US to my knowledge. I am probably wrong. But I cannot think of any case where an overwhelming mob/demonstrations have thrown a politician out of office by surpassing the police and washinton security. I cannot remember to ever have read about something like that in modern American history. It probably have happened in America prior to 1850.
No, but reality makes it a bad system.
I see the strenghts of all systems, including communism in China for example.
Americans tend to watch capitalis democracy as the only option. American politics and governance is becoming dogmatic, and always curses other ideas such a socialism or communism or any other alternatives, even as democracy in America is not only corrupted but rotten from the core out.