I've read the US Constitution, a couple of times actually, and it always seemed to me that the 'the country was founded in such a great document before it was sent down the drain' crowd has been busier parroting political spin than reading a very short text.

The constitution is just the basic framework for setting up the government. Virtually all of it deals with the top structure and responsibilities of the three government branches. As far as I can tell that's still pretty much the same.
Then it proscribes a process for how everything else is to be set up i.e. bills are approved by majority in Congress and signed by the President, after which they are laws. When there is a question or dispute, there is the supreme court established by the Constitution without any specifics to for example the number of its members (and any other courts the Congress may choose to establish) to settle what's right and what's wrong.

In my opinion anybody who thinks the skeleton of government from the US Constitution can be a functioning body is developmentally stuck in pre-teen years. The truth is that US has never ever had a government like that, before or after the Constitution.

US is what it is today because of the Constitution and because of the way people have voted. If you don't like the country as it is today you've got to change at least one of these two.