I don’t have enough time to summarize this excellent Article from Five Thirty Eight, but you should go read it. Politicians and others like to complain that elections are rigged, but this article says that the real rigging of our elections is being done by the voters themselves. It is short and easy to read — go read it.
My only complaint against the article is that it is short on solutions. It mentions changing to non-partisan primaries only in passing, even though this system is working very well in three states now. It also dismisses non-partisan redistricting as not helping enough, but I say that the problem is so serious that every little bit of help is required.