The Congress has never consistently functioned well, I'm not entirely convinced it's designed to. For the current mess, both in Congress and American politics in general, probably the most influential source is Newt Gingrich's electioneering policy of attacking wedges and saying anything you have to to get headlines without regards to the truthfulness of your statements. That's what reshaped the Republican party to be particularly welcoming to extremists, popularized science denial, and led to the modern wave of Christian Nationalism.