WTF happened to good government in the USA?
A few things come to mind, in reverse chronological order. Most recent, the Obama administration passing the ACA without any Republican support using a legal but marginally ethical procedure. IMHO, that burned any remaining bridges between the two parties and they haven't cooperated ever since.
Before that, the chaos after the US invasion of Iraq and Afghanistan. The invasions pretty broad support at the start but the blood bath afterwards (and the slow reveal that the invasions were based on false pretenses) really soured a lot of people on the GOP.
Before that, the 2000 election results. The SCOTUS decision to cut off the recounts also soured many Democrats from ever wanting to work with Republicans, no matter what. That's the converse of the ACA procedure.
And the first major blow came with the Clinton impeachment process. Many viewed that as a purely political attack and again, soured many Democrats from ever being willing to work with Republicans.
Add it all up and everyone has an axe to grind and a reason to want to grind their opponents into the mud. Neither party seems at all willing to debate issues on their merits. It's all about denying their opponents a victory at all costs.
The closeness of US elections doesn't help. I'm sure the political scientists can explain why having a closely divided electorate enhances partisanship. California is under complete Democratic control right now and Sacramento is pretty calm. There's no reason to have a noisy battle and every reason to cooperate. Not being a Democrat, I'm not sure I'm entirely happy with that situation but it is peaceful.