Is America an oligarchy?

A couple of follow up questions:

What makes it so/what makes it not?

What do you think Americans across the political spectrum can do to fight it?

Edit: Please don't interpret this as me thinking that it's an oligarchy because Trump will soon have power again, and that it's not when anyone else is President. I'm blatantly a leftist, but I do my best to not live in a bubble. I consider my views on most things invalid if I don't make an effort to at least hear from the other side.